The Allied Powers were the coalition of states that fought against the Central Powers during the First World War. The principal Allied powers included France, Britain and its empire, Russia until 1917, Serbia, Belgium, Japan, Italy from 1915 and the United States from 1917, along with numerous other countries that entered the conflict at different times. The coalition was not a single unified organisation with identical political objectives. Different governments joined for different reasons and pursued different strategic interests.
Britain and France were central western Allied powers, Russia fought primarily against Germany and Austria-Hungary in the east until its withdrawal, Italy fought Austria-Hungary after changing sides in 1915, and the United States entered later and provided major economic and military resources. The term Allies therefore describes a wartime coalition rather than a single political bloc with one completely shared programme.
Britain entered the war on 4 August 1914 after Germany invaded neutral Belgium and because British leaders regarded the European balance of power and the security of the Channel as important strategic interests. Britain possessed a powerful navy and an enormous empire, allowing it to mobilise personnel and resources from Canada, Australia, New Zealand, India, Africa and other territories. British naval power was crucial to the blockade of Germany and the protection of Allied maritime communications. Britain also fought on the Western Front and in the Middle East, Africa and the Dardanelles. The British Empire's participation made the conflict global and meant that soldiers from many territories served in a war whose strategic decisions were made primarily by European governments.
France was one of the principal Allied military powers and fought Germany throughout the conflict. France's strategic position was particularly dangerous because the German border was close to major French industrial and population centres. French forces fought in the major battles of the Western Front, including the First Battle of the Marne, Verdun and the Second Battle of the Marne. France suffered enormous military and civilian losses, while large areas of northeastern France were occupied or devastated. French military strategy increasingly depended on coordination with Britain and later the United States. By 1918, Allied command became more unified under Ferdinand Foch, helping coordinate major counteroffensives against German forces.
Russia entered the war on the Allied side after Austria-Hungary declared war on Serbia. Russia regarded itself as an important supporter of Serbia and sought to maintain influence in the Balkans. Russian forces launched offensives against Germany and Austria-Hungary in 1914, achieving some early successes against Austria-Hungary but suffering a major defeat against Germany at Tannenberg. Russia remained a major participant until revolutionary upheaval in 1917 transformed the state. The Bolshevik government then negotiated the Treaty of Brest Litovsk, signed in March 1918, withdrawing Russia from the war. Russia's departure allowed Germany to transfer substantial forces from the Eastern Front to the west, although the resulting German offensive ultimately failed.
Italy's position demonstrates that wartime coalitions could change. Italy had been a member of the Triple Alliance with Germany and Austria-Hungary before the war but declared neutrality in 1914, arguing that the alliance was defensive and Austria-Hungary had initiated the conflict. In 1915 Italy joined the Allies under the Treaty of London, which promised territorial gains at the expense of Austria-Hungary. Italian forces then fought a series of battles along the mountainous Italian Front. The fighting was extremely costly and included repeated offensives along the Isonzo River. In 1917 Italy suffered a major defeat at Caporetto but stabilised its front. In October and November 1918, Italian forces achieved a decisive victory at Vittorio Veneto as Austria-Hungary collapsed.
The United States entered the war in April 1917. American neutrality during the early years of the conflict was challenged by German unrestricted submarine warfare, attacks on shipping and the Zimmermann Telegram, in which Germany proposed an alliance with Mexico in the event of war with the United States. President Woodrow Wilson requested a declaration of war against Germany in April 1917. American forces required time to mobilise and train, but substantial US troops entered France in 1918.
American financial and industrial resources also strengthened the Allied war effort before large numbers of US soldiers arrived. The American contribution was particularly important during the final phase of the war, when Germany was attempting to win before the full weight of US manpower could be deployed.
Other Allied participants included Japan, which entered the war in 1914 and captured German possessions in East Asia and the Pacific, as well as Romania, Greece, Portugal, Belgium, Serbia and several other states. Japan's participation was linked to its alliance with Britain and its interest in expanding its position in East Asia. Romania joined the Allies in 1916 but suffered rapid military setbacks before recovering alongside later Allied advances.
Greece eventually joined the Allies in 1917 after a prolonged political crisis over neutrality. The diversity of Allied participants meant that the coalition covered several continents and possessed enormous combined resources. Colonial troops and labourers from Asia, Africa and other territories also made substantial contributions to Allied military and logistical efforts.
The Allied Powers ultimately defeated the Central Powers in 1918. Their advantages included greater access to global resources, maritime control, industrial capacity and, after 1917, American economic and military support. Allied victory was not inevitable throughout the war. Germany and its allies achieved major successes, particularly on the Eastern Front and in 1915 against Serbia. The Allied position remained precarious during several stages.
The final outcome resulted from cumulative military pressure, economic blockade, German exhaustion, the collapse of Austria-Hungary, Bulgaria and the Ottoman Empire, and the failure of Germany's 1918 offensives. The Allied coalition then shaped the post-war settlement through peace treaties and the creation of new international arrangements, although the different objectives of the Allied governments produced substantial disagreements over territory, reparations, security and self determination.
