1914–1918

Top Questions

Why did the U.S. enter World War I?

What was the main cause of World War I?

What countries fought in World War I?

Who won World War I?

News • 

‘Exceptionally rare’ World War I-era biplane returns to Long Island • July 31, 2026, 10:58 AM ET (Popular Science) 

World War I, an international conflict that in 1914–18 embroiled most of the nations of Europe along with Russia, the United States, the Middle East, and other regions. The war pitted the Central Powers—mainly Germany, Austria-Hungary, and Turkey—against the Allies—mainly France, Great Britain, Russia, Italy, Japan, and, from 1917, the United States. It ended with the defeat of the Central Powers. The war was virtually unprecedented in the slaughter, carnage, and destruction it caused.

World War I was one of the great watersheds of 20th-century geopolitical history. It led to the fall of four great imperial dynasties (in Germany, Russia, Austria-Hungary, and Turkey), resulted in the Bolshevik Revolution in Russia, and, in its destabilization of European society, laid the groundwork for World War II.

The outbreak of war

With Serbia already much aggrandized by the two Balkan Wars (1912–13, 1913), Serbian nationalists turned their attention back to the idea of “liberating” the South Slavs of Austria-Hungary. Colonel Dragutin Dimitrijević, head of Serbia’s military intelligence, was also, under the alias “Apis,” head of the secret society Union or Death, pledged to the pursuit of this pan-Serbian ambition. Believing that the Serbs’ cause would be served by the death of the Austrian archduke Franz Ferdinand, heir presumptive to the Austrian emperor Franz Joseph, and learning that the Archduke was about to visit Bosnia on a tour of military inspection, Apis plotted his assassination. Nikola Pašić, the Serbian prime minister and an enemy of Apis, heard of the plot and warned the Austrian government of it, but his message was too cautiously worded to be understood.

At 11:15 am on June 28, 1914, in the Bosnian capital, Sarajevo, Franz Ferdinand and his morganatic wife, Sophie, duchess of Hohenberg, were shot dead by a Bosnian Serb, Gavrilo Princip. The chief of the Austro-Hungarian general staff, Franz, Graf (count) Conrad von Hötzendorf, and the foreign minister, Leopold, Graf von Berchtold, saw the crime as the occasion for measures to humiliate Serbia and so to enhance Austria-Hungary’s prestige in the Balkans. Conrad had already (October 1913) been assured by William II of Germany’s support if Austria-Hungary should start a preventive war against Serbia. This assurance was confirmed in the week following the assassination, before William, on July 6, set off upon his annual cruise to the North Cape, off Norway.

The Austrians decided to present an unacceptable ultimatum to Serbia and then to declare war, relying on Germany to deter Russia from intervention. Though the terms of the ultimatum were finally approved on July 19, its delivery was postponed to the evening of July 23, since by that time the French president, Raymond Poincaré, and his premier, René Viviani, who had set off on a state visit to Russia on July 15, would be on their way home and therefore unable to concert an immediate reaction with their Russian allies. When the delivery was announced, on July 24, Russia declared that Austria-Hungary must not be allowed to crush Serbia.Britannica QuizPick Your Battles Quiz

Serbia replied to the ultimatum on July 25, accepting most of its demands but protesting against two of them—namely, that Serbian officials (unnamed) should be dismissed at Austria-Hungary’s behest and that Austro-Hungarian officials should take part, on Serbian soil, in proceedings against organizations hostile to Austria-Hungary. Though Serbia offered to submit the issue to international arbitration, Austria-Hungary promptly severed diplomatic relations and ordered partial mobilization.

Home from his cruise on July 27, William learned on July 28 how Serbia had replied to the ultimatum. At once he instructed the German Foreign Office to tell Austria-Hungary that there was no longer any justification for war and that it should content itself with a temporary occupation of Belgrade. But, meanwhile, the German Foreign Office had been giving such encouragement to Berchtold that already on July 27 he had persuaded Franz Joseph to authorize war against Serbia. War was in fact declared on July 28, and Austro-Hungarian artillery began to bombard Belgrade the next day. Russia then ordered partial mobilization against Austria-Hungary, and on July 30, when Austria-Hungary was riposting conventionally with an order of mobilization on its Russian frontier, Russia ordered general mobilization. Germany, which since July 28 had still been hoping, in disregard of earlier warning hints from Great Britain, that Austria-Hungary’s war against Serbia could be “localized” to the Balkans, was now disillusioned insofar as eastern Europe was concerned. On July 31 Germany sent a 24-hour ultimatum requiring Russia to halt its mobilization and an 18-hour ultimatum requiring France to promise neutrality in the event of war between Russia and Germany.

Both Russia and France predictably ignored these demands. On August 1 Germany ordered general mobilization and declared war against Russia, and France likewise ordered general mobilization. The next day Germany sent troops into Luxembourg and demanded from Belgium free passage for German troops across its neutral territory. On August 3 Germany declared war against France.

In the night of August 3–4 German forces invaded Belgium. Thereupon, Great Britain, which had no concern with Serbia and no express obligation to fight either for Russia or for France but was expressly committed to defend Belgium, on August 4 declared war against Germany.

Austria-Hungary declared war against Russia on August 5; Serbia against Germany on August 6; Montenegro against Austria-Hungary on August 7 and against Germany on August 12; France and Great Britain against Austria-Hungary on August 10 and on August 12, respectively; Japan against Germany on August 23; Austria-Hungary against Japan on August 25 and against Belgium on August 28.

Romania had renewed its secret anti-Russian alliance of 1883 with the Central Powers on February 26, 1914, but now chose to remain neutral. Italy had confirmed the Triple Alliance on December 7, 1912, but could now propound formal arguments for disregarding it: first, Italy was not obliged to support its allies in a war of aggression; second, the original treaty of 1882 had stated expressly that the alliance was not against England.

On September 5, 1914, Russia, France, and Great Britain concluded the Treaty of London, each promising not to make a separate peace with the Central Powers. Thenceforth, they could be called the Allied, or Entente, powers, or simply the Allies.

Quick FactsAlso called: First World War or Great WarDate: July 28, 1914 – November 11, 1918Participants: BulgariaFranceGermanyItalyJapanOttoman EmpirePortugalRussiaUnited KingdomUnited StatesMajor Events: Battle of GazaBattle of JutlandBattle of Morhange-SarrebourgBattle of VerdunEastern FrontKey People: Kemal AtatürkWinston ChurchillGeorges ClemenceauDavid Lloyd GeorgeWoodrow Wilson

The outbreak of war in August 1914 was generally greeted with confidence and jubilation by the peoples of Europe, among whom it inspired a wave of patriotic feeling and celebration. Few people imagined how long or how disastrous a war between the great nations of Europe could be, and most believed that their country’s side would be victorious within a matter of months. The war was welcomed either patriotically, as a defensive one imposed by national necessity, or idealistically, as one for upholding right against might, the sanctity of treaties, and international morality.

Forces and resources of the combatant nations in 1914

When war broke out, the Allied powers possessed greater overall demographic, industrial, and military resources than the Central Powers and enjoyed easier access to the oceans for trade with neutral countries, particularly with the United States.

The table shows the population, steel production, and armed strengths of the two rival coalitions in 1914.

resources	Central Powers	Allied Powers
population (in millions)	115.2	265.5
steel production (in millions of metric tons)	17.0	15.3
army divisions available for mobilization	146	212
modern battleships	20	39

All the initial belligerents in World War I were self-sufficient in food except Great Britain and Germany. Great Britain’s industrial establishment was slightly superior to Germany’s (17 percent of world trade in 1913 as compared with 12 percent for Germany), but Germany’s diversified chemical industry facilitated the production of ersatz, or substitute, materials, which compensated for the worst shortages ensuing from the British wartime blockade. The German chemist Fritz Haber was already developing a process for the fixation of nitrogen from air; this process made Germany self-sufficient in explosives and thus no longer dependent on imports of nitrates from Chile.

Of all the initial belligerent nations, only Great Britain had a volunteer army, and this was quite small at the start of the war. The other nations had much larger conscript armies that required three to four years of service from able-bodied males of military age, to be followed by several years in reserve formations. Military strength on land was counted in terms of divisions composed of 12,000–20,000 officers and men. Two or more divisions made up an army corps, and two or more corps made up an army. An army could thus comprise anywhere from 50,000 to 250,000 men.

The land forces of the belligerent nations at the outbreak of war in August 1914 are shown in the table.

World War I eventskeyboard_arrow_left

keyboard_arrow_right

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10

	country	regular divisions (with number of field armies)	other land forces	total manpower
Central Powers	Germany	98 (8)	27 Landwehr brigades	1,900,000
	Austria-Hungary	48 (6)		450,000
Allied Powers	Russia	102 (6)		1,400,000
	France	72 (5)		1,290,000
	Serbia	11 (3)		190,000
	Belgium	7 (1)	69,000 fortress troops	186,000
	Great Britain	6 (1)	14 territorial divisions*	120,000
*Restricted in 1914 to service at home.

The higher state of discipline, training, leadership, and armament of the German army reduced the importance of the initial numerical inferiority of the armies of the Central Powers. Because of the comparative slowness of mobilization, poor higher leadership, and lower scale of armament of the Russian armies, there was an approximate balance of forces between the Central Powers and the Allies in August 1914 that prevented either side from gaining a quick victory.

Germany and Austria also enjoyed the advantage of “interior lines of communication,” which enabled them to send their forces to critical points on the battlefronts by the shortest route. According to one estimate, Germany’s railway network made it possible to move eight divisions simultaneously from the Western Front to the Eastern Front in four and a half days.

Even greater in importance was the advantage that Germany derived from its strong military traditions and its cadre of highly efficient and disciplined regular officers. Skilled in directing a war of movement and quick to exploit the advantages of flank attacks, German senior officers were to prove generally more capable than their Allied counterparts at directing the operations of large troop formations.

Sea power was largely reckoned in terms of capital ships, or dreadnought battleships and battle cruisers having extremely large guns. Despite intensive competition from the Germans, the British had maintained their superiority in numbers, with the result that, in capital ships, the Allies had an almost two-to-one advantage over the Central Powers.

The strength of the two principal rivals at sea, Great Britain and Germany, is compared in the table.

type	British	German
dreadnought battleships	20	14
battle cruisers	9	4
pre-dreadnought battleships	39	22
armoured cruisers	34	9
cruisers	64	41
destroyers	301*	144
submarines	65	28
*Including Canadian, Australian, and New Zealand destroyers of all classes.

The numerical superiority of the British navy, however, was offset by the technological lead of the German navy in many categories, such as range-finding equipment, magazine protection, searchlights, torpedoes, and mines. Great Britain relied on the Royal Navy not only to ensure necessary imports of food and other supplies in wartime but also to sever the Central Powers’ access to the markets of the world. With superior numbers of warships, Great Britain could impose a blockade that gradually weakened Germany by preventing imports from overseas.

Technology of war in 1914

The planning and conduct of war in 1914 were crucially influenced by the invention of new weapons and the improvement of existing types since the Franco-German War of 1870–71. The chief developments of the intervening period had been the machine gun and the rapid-fire field artillery gun. The modern machine gun, which had been developed in the 1880s and ’90s, was a reliable belt-fed gun capable of sustained rates of extremely rapid fire; it could fire 600 bullets per minute with a range of more than 1,000 yards (900 metres). In the realm of field artillery, the period leading up to the war saw the introduction of improved breech-loading mechanisms and brakes. Without a brake or recoil mechanism, a gun lurched out of position during firing and had to be re-aimed after each round. The new improvements were epitomized in the French 75-millimetre field gun; it remained motionless during firing, and it was not necessary to readjust the aim in order to bring sustained fire on a target.

Machine guns and rapid-firing artillery, when used in combination with trenches and barbed-wire emplacements, gave a decided advantage to the defense, since these weapons’ rapid and sustained firepower could decimate a frontal assault by either infantry or cavalry.

There was a considerable disparity in 1914 between the deadly effectiveness of modern armaments and the doctrinal teachings of some armies. The South African War and the Russo-Japanese War had revealed the futility of frontal infantry or cavalry attacks on prepared positions when unaccompanied by surprise, but few military leaders foresaw that the machine gun and the rapid-firing field gun would force armies into trenches in order to survive. Instead, war was looked upon by many leaders in 1914 as a contest of national wills, spirit, and courage. A prime example of this attitude was the French army, which was dominated by the doctrine of the offensive. French military doctrine called for headlong bayonet charges of French infantrymen against the German rifles, machine guns, and artillery. German military thinking, under the influence of Alfred, Graf von Schlieffen, sought, unlike the French, to avoid frontal assaults but rather to achieve an early decision by deep flanking attacks; and at the same time to make use of reserve divisions alongside regular formations from the outset of war. The Germans paid greater attention to training their officers in defensive tactics using machine guns, barbed wire, and fortifications.

The initial stages of the war

Initial strategies

The Schlieffen Plan

Years before 1914, successive chiefs of the German general staff had been foreseeing Germany’s having to fight a war on two fronts at the same time, against Russia in the east and France in the west, whose combined strength was numerically superior to the Central Powers’. The elder Helmuth von Moltke, chief of the German general staff from 1858 to 1888, decided that Germany should stay at first on the defensive in the west and deal a crippling blow to Russia’s advanced forces before turning to counterattack the French advance. His immediate successor, Alfred von Waldersee, also believed in staying on the defensive in the west. Alfred, Graf von Schlieffen, who served as chief of the German general staff from 1891 to 1905, took a contrary view, and it was the plan he developed that was to guide Germany’s initial wartime strategy. Schlieffen realized that on the outbreak of war Russia would need six full weeks to mobilize and assemble its vast armies, given the immense Russian countryside and population, the sparsity of the rail network, and the inefficiency of the government bureaucracy. Taking advantage of this fact, Schlieffen planned to initially adopt a purely defensive posture on the Eastern Front with a minimal number of troops facing Russia’s slowly gathering armies. Germany would instead concentrate almost all of its troops in the west against France and would seek to bypass France’s frontier fortifications by an offensive through neutral Belgium to the north. This offensive would sweep westward and then southward through the heart of northern France, capturing the capital and knocking that country out of the war within a few weeks. Having gained security in the west, Germany would then shift its troops to the east and destroy the Russian menace with a similar concentration of forces.

By the time of his retirement in 1905, Schlieffen had elaborated a plan for a great wheeling movement of the right (northern) wing of the German armies not only through central Belgium but also, in order to bypass the Belgian fortresses of Liège and Namur in the Meuse valley, through the southernmost part of the Netherlands. With their right wing entering France near Lille, the Germans would continue to wheel westward until they were near the English Channel; they would then turn southward so as to sever the French armies’ line of retreat from France’s eastern frontier to the south; and the outermost arc of the wheel would sweep southward west of Paris, in order to avoid exposing the German right flank to a counterstroke launched from the city’s outskirts. If the Schlieffen Plan succeeded, Germany’s armies would simultaneously encircle the French army from the north, overrun all of northeastern France, and capture Paris, thus forcing France into a humiliating surrender. The large wheeling movement that the plan envisaged required correspondingly large forces for its execution, in view of the need to keep up the numerical strength of the long-stretched marching line and the need to leave adequate detachments on guard over the Belgian fortresses that had been bypassed. Accordingly, Schlieffen allocated nearly seven-eighths of Germany’s available troop strength to the execution of the wheeling movement by the right and centre wings, leaving only one-eighth to face a possible French offensive on Germany’s western frontier. Thus, the maximum of strength was allocated to the wheel’s edge—that is, to the right. Schlieffen’s plan was observed by the younger Helmuth von Moltke, who became chief of the general staff in 1906. Moltke was still in office when war broke out in 1914.Britannica QuizPick Your Battles Quiz

Eastern Front strategy, 1914

Russian Poland, the westernmost part of the Russian Empire, was a thick tongue of land enclosed to the north by East Prussia, to the west by German Poland (Poznania) and by Silesia, and to the south by Austrian Poland (Galicia). It was thus obviously exposed to a two-pronged invasion by the Central Powers, but the Germans, apart from their grand strategy of crushing France before attempting anything against Russia, took note of the poverty of Russian Poland’s transportation network and so were disinclined to overrun that vulnerable area prematurely. Austria-Hungary, however, whose frontier with Russia lay much farther east than Germany’s and who was moreover afraid of disaffection among the Slav minorities, urged some immediate action to forestall a Russian offensive. Moltke therefore agreed to the Austrian general staff’s suggestion for a northeastward thrust by the Austrian army into Russian Poland—the more readily because it would occupy the Russians during the crisis in France.

The Russians, for their part, would have preferred to concentrate their immediately available forces against Austria and to leave Germany undisturbed until their mobilization should have been completed. The French were anxious to relieve the German pressure against themselves, however, and so they persuaded the Russians to undertake an offensive involving two armies against the Germans in East Prussia simultaneously with one involving four armies against the Austrians in Galicia. The Russian army, whose proverbial slowness and unwieldy organization dictated a cautious strategy, thus undertook an extra offensive against East Prussia that only an army of high mobility and tight organization could have hoped to execute successfully.

The strategy of the Western Allies, 1914

For some 30 years after 1870, considering the likelihood of another German war, the French high command had subscribed to the strategy of an initial defensive to be followed by a counterstroke against the expected invasion: a great system of fortresses was created on the frontier, but gaps were left in order to “canalize” the German attack. France’s alliance with Russia and its entente with Great Britain, however, encouraged a reversal of plan, and after the turn of the century a new school of military thinkers began to argue for an offensive strategy. The advocates of the offensive à l’outrance (“to the utmost”) gained control of the French military machine, and in 1911 a spokesman of this school, General J.-J.-C. Joffre, was designated chief of the general staff. He sponsored the notorious Plan XVII, with which France went to war in 1914.

Plan XVII gravely underestimated the strength that the Germans would deploy against France. Accepting the possibility that the Germans might employ their reserve troops along with regular troops at the outset, Plan XVII estimated the strength of the German army in the west at a possible maximum of 68 infantry divisions. The Germans actually deployed the equivalent of 83 1/2 divisions, counting Landwehr (reserve troops) and Ersatz (low-grade substitute troops) divisions, but French military opinion ignored or doubted this possibility; during the war’s crucial opening days, when the rival armies were concentrating and moving forward, the French Intelligence counted only Germany’s regular divisions in its estimates of the enemy strength. This was a serious miscalculation. Plan XVII also miscalculated the direction and scope of the coming onslaught: though it foresaw an invasion through Belgium, it assumed that the Germans would take the route through the Ardennes, thereby exposing their communications to attack. Basing itself on the idea of an immediate and general offensive, Plan XVII called for a French thrust toward the Saar into Lorraine by the 1st and 2nd armies, while on the French left (the north) the 3rd and 5th armies, facing Metz and the Ardennes, respectively, stood ready either to launch an offensive between Metz and Thionville or to strike from the north at the flank of any German drive through the Ardennes. When war broke out, it was taken for granted that the small British Expeditionary Force (BEF) under Sir John French should be used as an adjunct to France’s forces, more or less as the French might see fit. It is clearly evident that the French were oblivious to the gigantic German offensive that was being aimed at their left (northern) wing.

The war in the west, 1914

The German invasion

For the smooth working of their plan for the invasion of France, the Germans had preliminarily to reduce the ring fortress of Liège, which commanded the route prescribed for their 1st and 2nd armies and which was the foremost stronghold of the Belgian defenses. German troops crossed the frontier into Belgium on the morning of August 4. Thanks to the resolution of a middle-aged staff officer, Erich Ludendorff, a German brigade occupied the town of Liège itself in the night of August 5–6 and the citadel on August 7, but the surrounding forts held out stubbornly until the Germans brought their heavy howitzers into action against them on August 12. These 420-millimetre siege guns proved too formidable for the forts, which one by one succumbed. The vanguard of the German invasion was already pressing the Belgian field army between the Gete River and Brussels, when the last of the Liège forts fell on August 16. The Belgians then withdrew northward to the entrenched camp of Antwerp. On August 20 the German 1st Army entered Brussels while the 2nd Army appeared before Namur, the one remaining fortress barring the Meuse route into France.

The initial clashes between the French and German armies along the Franco-German and Franco-Belgian frontiers are collectively known as the Battle of the Frontiers. This group of engagements, which lasted from August 14 until the beginning of the First Battle of the Marne on September 6, was to be the largest battle of the war and was perhaps the largest battle in human history up to that time, given the fact that a total of more than two million troops were involved.

The planned French thrust into Lorraine, totaling 19 divisions, started on August 14 but was shattered by the German 6th and 7th armies in the Battle of Morhange-Sarrebourg (August 20–22). Yet this abortive French offensive had an indirect effect on the German plan. For when the French attack in Lorraine developed, Moltke was tempted momentarily to postpone the right-wing sweep and instead to seek a victory in Lorraine. This fleeting impulse led him to divert to Lorraine the six newly formed Ersatz divisions that had been intended to increase the weight of his right wing. This was the first of several impromptu decisions by Moltke that were to fatally impair the execution of the Schlieffen Plan.

Meanwhile, the German imperial princes who commanded armies on the Germans’ left (southern) wing in Lorraine were proving unwilling to forfeit their opportunity for personal glory. Crown Prince Rupert of Bavaria on August 20 ordered his 6th Army to counterattack instead of continuing to fall back before the French advance as planned, and Crown Prince William of Germany ordered his 5th Army to do the same. The strategic result of these unplanned German offensives was merely to throw the French back onto a fortified barrier that both restored and augmented their power of resistance. Thus, the French were soon afterward enabled to dispatch troops to reinforce their left flank—a redistribution of strength that was to have far-reaching results in the decisive Battle of the Marne.

While this seesaw campaign in Lorraine was taking place, more decisive events were occurring to the northwest. The German attack on Liège had awakened Joffre to the reality of a German advance through Belgium, but not to its strength or to the wideness of its sweep. In preparing a counterattack against the German advance through Belgium, Joffre envisaged a pincer movement, with the French 3rd and 4th armies on the right and the 5th, supported by the BEF, on the left, to trap the Germans in the Meuse–Ardennes area south of Liège. The fundamental flaw in this new French plan was that the Germans had deployed about 50 percent more troops than the French had estimated, and for a vaster enveloping movement. Consequently, while the right-hand claw of the French pincer (23 divisions) collided with the German 5th and 4th armies (20 divisions) in the Ardennes and was thrown back, the left-hand claw (13 French and four British divisions) found itself nearly trapped between the German 1st and 2nd armies, with a total of 30 divisions, on the one hand, and the 3rd, on the other. As the French 5th Army, under General Charles Lanrezac, was checked in its offensive south of the Sambre River by a German attack on August 21, the British, who reached Mons on August 22, at first agreed to stand there to cover Lanrezac’s left; but on August 23 news of the fall of Namur and of the German 3rd Army’s presence near Dinant induced Lanrezac to wisely order a general retreat; and on August 24 the British began their retreat from Mons, just in time to escape envelopment by the German 1st Army’s westward march around their unprotected left flank.

At last Joffre realized the truth and the utter collapse of Plan XVII. Resolution was his greatest asset, and with imperturbable coolness he formed a new plan out of the wreckage. Joffre decided to swing the Allied centre and left back southwestward from the Belgian frontier to a line pivoted on the French fortress of Verdun and at the same time to withdraw some strength from the right wing so as to be able to station a newly created 6th Army on the extreme left, north of Paris. This plan might, in turn, have collapsed if the Germans had not themselves departed from Schlieffen’s original plan due to a combination of Moltke’s indecisiveness, poor communications between his headquarters and the field army commanders of the German right wing, and Moltke’s resulting confusion about the developing tactical situation. In the first place, the German right wing was weakened by the subtraction of 11 divisions; four were detached to watch Antwerp and to invest French fortresses near the Belgian frontier, instead of using reserve and Ersatz troops for this as earlier intended, and seven more regular divisions were transferred to check the Russian advance into East Prussia (see below). In the second place, Alexander von Kluck, in command of the 1st Army, did in fact wheel inward north of Paris rather than southwest of the city.

Kluck’s change of direction meant the inevitable abandonment of the original wide sweep around the far (western) side of Paris. Now the flank of this wheeling German line would pass the near side of Paris and across the face of the Paris defenses into the valley of the Marne River. The premature inward wheel of Kluck’s 1st Army before Paris had been reached thus exposed the German extreme right wing to a flank attack and a possible counter-envelopment. On September 4 Moltke decided to abandon the original Schlieffen Plan and substituted a new one: the German 4th and 5th armies should drive southeastward from the Ardennes into French Lorraine west of Verdun and then converge with the southwestward advance of the 6th and 7th armies from Alsace against the Toul–Épinal line of fortifications, so as to envelop the whole French right wing; the 1st and 2nd armies, in the Marne valley, should stand guard, meanwhile, against any French countermove from the vicinity of Paris. But such an Allied countermove had already begun before the new German plan could be put into effect.

The First Battle of the Marne

Already on September 3, General J.-S. Gallieni, the military governor of Paris, had guessed the significance of the German 1st Army’s swing inward to the Marne east of Paris. On September 4 Joffre, convinced by Gallieni’s arguments, decisively ordered his whole left wing to turn about from their retreat and to begin a general offensive against the Germans’ exposed right flank on September 6. The French 6th Army, under M.-J. Maunoury, forewarned by Gallieni, had actually begun attacking on September 5, and its pressure caused Kluck finally to engage the whole 1st Army in support of his right flank when he was still no farther up the Marne valley than Meaux, with nothing but a cavalry screen stretched across the 30 miles between him and Karl von Bülow’s 2nd Army (at Montmirail). While the French 5th Army was turning to attack Bülow, the BEF (between the 5th and the 6th armies) was still continuing its retreat for another day, but on September 9 Bülow learned that the British too had turned and were advancing into the gap between him and Kluck. He therefore ordered the 2nd Army to retreat, thus obliging Kluck to do likewise with the 1st. The counterattack of the French 5th and 6th armies and the BEF developed into a general counterattack by the entire left and centre of the French army. This counterattack is known as the First Battle of the Marne. By September 11 the German retreat extended to all the German armies.

There were several reasons for this extraordinary turn of events. Chief among them was the utter exhaustion of the German soldiery of the right wing, some of whom had marched more than 150 miles (240 kilometres) under conditions of frequent battle. Their fatigue was ultimately a by-product of the Schlieffen Plan itself, for while the retreating French had been able to move troops by rail to various points within the circle formed by the front, the German troops had found their advance hampered by demolished bridges and destroyed rail lines. Their food and ammunition supply was consequently restricted, and the troops also had to make their advance by foot. Moreover, the Germans had underestimated the resilient spirit of the French troops, who had maintained their courage and morale and their confidence in their commanders. This fact was strikingly evidenced by the comparatively small number of prisoners taken by the Germans in the course of what was undeniably a precipitous French retreat.

Meanwhile, the assault by the German 6th and 7th armies on the defenses of the French eastern frontier had already proved a predictably expensive failure, and the German attempt at a partial envelopment pivoted on Verdun was abandoned. The German right wing withdrew northward from the Marne and made a firm stand along the Lower Aisne River and the Chemin des Dames ridge. Along the Aisne the preponderant power of the defense over the offense was reemphasized as the Germans repelled successive Allied attacks from the shelter of trenches. The First Battle of the Aisne marked the real beginning of trench warfare on the Western Front. Both sides were in the process of discovering that, in lieu of frontal assaults for which neither had the manpower readily available, the only alternative was to try to overlap and envelop the other’s flank, in this case the one on the side pointing toward the North Sea and the English Channel. Thus began the “Race to the Sea,” in which the developing trench networks of both sides were quickly extended northwestward until they reached the Atlantic at a point just inside coastal Belgium, west of Ostend.

The First Battle of the Marne succeeded in pushing the Germans back for a distance of 40 to 50 miles and thus saved the capital city of Paris from capture. In this respect it was a great strategic victory, since it enabled the French to renew their confidence and to continue the war. But the great German offensive, though unsuccessful in its object of knocking France out of the war, had enabled the Germans to capture a large portion of northeastern France. The loss of this heavily industrialized region, which contained much of the country’s coal, iron, and steel production, was a serious blow to the continuation of the French war effort.

The Belgian army, meanwhile, had fallen back to the fortress city of Antwerp, which ended up behind the German lines. The Germans began a heavy bombardment of Antwerp on September 28, and Antwerp surrendered to the Germans on October 10.

After the failure of his first two attempts to turn the Germans’ western flank (one on the Somme, the other near Arras), Joffre obstinately decided to try again yet farther north with the BEF—which in any case was being moved northward from the Aisne. The BEF, accordingly, was deployed between La Bassée and Ypres, while on the left the Belgians—who had wisely declined to participate in the projected attack—continued the front along the Yser down to the Channel. Erich von Falkenhayn, however, who on September 14 had succeeded Moltke as chief of the German general staff, had foreseen what was coming and had prepared a counterplan: one of his armies, transferred from Lorraine, was to check the expected offensive, while another was to sweep down the coast and crush the attackers’ left flank. The British attack was launched from Ypres on October 19, the German thrust the next day. Though the Belgians of the Yser had been under increasing pressure for two days already, both Sir John French and Ferdinand Foch, Joffre’s deputy in the north, were slow to appreciate what was happening to their “offensive,” but in the night of October 29–30 the Belgians had to open the sluices on the Yser River to save themselves by flooding the Germans’ path down the coast. The Battle of Ypres had its worst crises on October 31 and November 11 and did not die down into trench warfare until November 22.

By the end of 1914 the casualties the French had so far sustained in the war totaled about 380,000 killed and 600,000 wounded; the Germans had lost a slightly smaller number. With the repulse of the German attempt to break through at the Battle of Ypres, the strained and exhausted armies of both sides settled down into trench warfare. The trench barrier was consolidated from the Swiss frontier to the Atlantic; the power of modern defense had triumphed over the attack, and stalemate ensued. The military history of the Western Front during the next three years was to be a story of the Allies’ attempts to break this deadlock.

The Eastern and other fronts, 1914