The Western Front was the main theatre of war during the First World War. Following the outbreak of war in August 1914, the German Army opened the Western Front by invading Luxembourg and Belgium, then gaining military control of important industrial regions in France. The German advance was halted with the Battle of the Marne. Following the Race to the Sea, both sides dug in along a meandering line of fortified trenches, stretching from the North Sea to the Swiss frontier with France, which changed little except during early 1917 and in 1918.
Between 1915 and 1917 there were several offensives along this front. The attacks employed massive artillery bombardments and massed infantry advances. Entrenchments, machine gun emplacements, barbed wire and artillery repeatedly inflicted severe casualties during attacks and counter-attacks and no significant advances were made. Among the most costly of these offensives were the Battle of Verdun, in 1916, with a combined 700,000 casualties (estimated), the Battle of the Somme, also in 1916, with more than a million casualties (estimated), and the Battle of Passchendaele (Third Battle of Ypres), in 1917, with 487,000 casualties (estimated).
To break the deadlock of trench warfare on the Western Front, both sides tried new military technology, including poison gas, aircraft, and tanks. The adoption of better tactics and the cumulative weakening of the armies in the west led to the return of mobility in 1918. The German Spring Offensive of 1918 was made possible by the Treaty of Brest-Litovsk that ended the war of the Central Powers against Russia and Romania on the Eastern Front. Using short, intense "hurricane" bombardments and infiltration tactics, the German armies moved nearly 100 kilometres (60 miles) to the west, the deepest advance by either side since 1914, but the result was indecisive.
The unstoppable advance of the Allied armies during the Hundred Days Offensive of 1918 caused a sudden collapse of the German armies and persuaded the German commanders that defeat was inevitable. The German government surrendered in the Armistice of 11 November 1918, and the terms of peace were settled by the Treaty of Versailles in 1919.
At the outbreak of the First World War, the German Army, with seven field armies in the west and one in the east, executed a modified version of the Schlieffen Plan, moving quickly through neutral Belgium to attack France, and then turning southwards to encircle the French Army and trap it on the German border. The Western Front was the place where the most powerful military forces in Europe, the German and French armies, met and where the war was decided. Belgian neutrality had been guaranteed by Britain under the Treaty of London, 1839; this caused Britain to join the war at the expiration of its ultimatum at midnight on 4 August. Armies under German generals Alexander von Kluck and Karl von Bülow attacked Belgium on 4 August 1914. Luxembourg had been occupied without opposition on 2 August. The first battle in Belgium was the Siege of Liège, which lasted from 5–16 August. Liège was well fortified and surprised the German Army under Bülow with its level of resistance. German heavy artillery was able to demolish the main forts within a few days. Following the fall of Liège, most of the Belgian field army retreated to Antwerp, leaving the garrison of Namur isolated, with the Belgian capital, Brussels, falling to the Germans on 20 August. Although the German army bypassed Antwerp, it remained a threat to their flank. Another siege followed at Namur, lasting from about 20–23 August.
The French deployed five armies on the frontier. The French Plan XVII was intended to bring about the capture of Alsace-Lorraine. On 7 August, the VII Corps attacked Alsace to capture Mulhouse and Colmar. The main offensive was launched on 14 August with the First and Second Armies attacking toward Sarrebourg-Morhange in Lorraine. In keeping with the Schlieffen Plan, the Germans withdrew slowly while inflicting severe losses upon the French. The French Third and Fourth Armies advanced toward the Saar River and attempted to capture Saarburg, attacking Briey and Neufchateau but were repulsed. The French VII Corps captured Mulhouse after a brief engagement on 7 August but German reserve forces engaged them in the Battle of Mulhouse and forced a French retreat.
The German Army swept through Belgium, executing civilians and razing villages. The application of "collective responsibility" against a civilian population further galvanised the allies. Newspapers condemned the German invasion, violence against civilians and destruction of property, which became known as the "Rape of Belgium."[d] After marching through Belgium, Luxembourg and the Ardennes, the Germans advanced into northern France in late August, where they met the French Army, under Joseph Joffre, and the divisions of the British Expeditionary Force under Field Marshal Sir John French. A series of engagements known as the Battle of the Frontiers ensued, which included the Battle of Charleroi and the Battle of Mons. In the former battle the French Fifth Army was almost destroyed by the German 2nd and 3rd Armies and the latter delayed the German advance by a day. A general Allied retreat followed, resulting in more clashes at the Battle of Le Cateau, the Siege of Maubeuge and the Battle of St. Quentin (also called the First Battle of Guise).
The German Army came within 70 km (43 mi) of Paris but at the First Battle of the Marne (6–12 September), French and British troops were able to force a German retreat by exploiting a gap which appeared between the 1st and 2nd Armies, ending the German advance into France. The German Army retreated north of the Aisne River and dug in there, establishing the beginnings of a static western front that was to last for the next three years. Following this German retirement, the opposing forces made reciprocal outflanking manoeuvres, known as the Race for the Sea and quickly extended their trench systems from the Swiss frontier to the North Sea. The territory occupied by Germany held 64 percent of French pig-iron production, 24 percent of its steel manufacturing and 40 percent of the coal industry – dealing a serious blow to French industry.
On the Entente side (those countries opposing the German alliance), the final lines were occupied with the armies of each nation defending a part of the front. From the coast in the north, the primary forces were from Belgium, the British Empire and then France. Following the Battle of the Yser in October, the Belgian army controlled a 35 km (22 mi) length of West Flanders along the coast, known as the Yser Front, along the Yser river and the Yperlee canal, from Nieuwpoort to Boesinghe. Meanwhile, the British Expeditionary Force (BEF) occupied a position on the flank, having occupied a more central position.
From 19 October until 22 November, the German forces made their final breakthrough attempt of 1914 during the First Battle of Ypres, which ended in a mutually-costly stalemate. After the battle, Erich von Falkenhayn judged that it was no longer possible for Germany to win the war by purely military means and on 18 November 1914 he called for a diplomatic solution. The Chancellor, Theobald von Bethmann-Hollweg; Generalfeldmarschall Paul von Hindenburg, commanding Ober Ost (Eastern Front high command); and his deputy, Erich Ludendorff, continued to believe that victory was achievable through decisive battles. During the Lodz offensive in Poland (11–25 November), Falkenhayn hoped that the Russians would be made amenable to peace overtures. In his discussions with Bethmann-Hollweg, Falkenhayn viewed Germany and Russia as having no insoluble conflict and that the real enemies of Germany were France and Britain. A peace with only a few annexations of territory also seemed possible with France and that with Russia and France out of the war by negotiated settlements, Germany could concentrate on Britain and fight a long war with the resources of Europe at its disposal. Hindenburg and Ludendorff continued to believe that Russia could be defeated by a series of battles which cumulatively would have a decisive effect, after which Germany could finish off France and Britain.
Trench warfare in 1914, while not new, quickly became much improved and provided a very high degree of defense. According to two prominent historians:
Between the coast and the Vosges was a westward bulge in the trench line, named the Noyon salient for the captured French town at the maximum point of advance near Compiègne. Joffre's plan for 1915 was to attack the salient on both flanks to cut it off. The Fourth Army had attacked in Champagne from 20 December 1914 – 17 March 1915 but the French were not able to attack in Artois at the same time. The Tenth Army formed the northern attack force and was to attack eastwards into the Douai plain across a 16-kilometre (9.9 mi) front between Loos and Arras. On 10 March, as part of the larger offensive in the Artois region, the British Army fought the Battle of Neuve Chapelle to capture Aubers Ridge. The assault was made by four divisions along a 2 mi (3.2 km) front. Preceded by a surprise bombardment lasting only 35 minutes, the initial assault made rapid progress and the village was captured within four hours. The advance then slowed because of supply and communication difficulties. The Germans brought up reserves and counter-attacked, forestalling the attempt to capture the ridge. Since the British had used about one-third of their supply of artillery ammunition, General Sir John French blamed the failure on the shortage of ammunition, despite the early success.
All sides had signed the Hague Conventions of 1899 and 1907, which prohibited the use of chemical weapons in warfare. In 1914, there had been small-scale attempts by both the French and Germans to use various tear gases, which were not strictly prohibited by the early treaties but which were also ineffective. The first use of more lethal chemical weapons on the Western Front was against the French near the Belgian town of Ypres. The Germans had already deployed gas against the Russians in the east at the Battle of Bolimów.
Despite the German plans to maintain the stalemate with the French and British, Albrecht, Duke of Württemberg, commander of the 4th Army planned an offensive at Ypres, site of the First Battle of Ypres in November 1914. The Second Battle of Ypres, April 1915, was intended to divert attention from offensives in the Eastern Front and disrupt Franco-British planning. After a two-day bombardment, the Germans released a cloud of 168 long tons (171 t) of chlorine gas onto the battlefield. Though primarily a powerful irritant, it can asphyxiate in high concentrations or prolonged exposure. Being heavier than air, the gas crept across no man's land and drifted into the French trenches. The green-yellow cloud started killing some defenders and those in the rear fled in panic, creating an undefended 3.7-mile (6 km) gap in the Allied line. The Germans were unprepared for the level of their success and lacked sufficient reserves to exploit the opening. Canadian troops on the right drew back their left flank and halted the German advance. The gas attack was repeated two days later and caused a 3.1 mi (5 km) withdrawal of the Franco-British line but the opportunity had been lost.
The success of this attack would not be repeated, as the Allies countered by introducing gas masks and other <