The First World War was a global conflict fought primarily between the Allied Powers and the Central Powers from 1914 to 1918. It began in Europe after the assassination of Archduke Franz Ferdinand of Austria Hungary in Sarajevo on 28 June 1914, but its origins involved longer term rivalries concerning alliances, nationalism, imperial competition, military planning and tensions in southeastern Europe.
Austria Hungary declared war on Serbia in July, and Germany, Russia, France and Britain became involved through diplomatic commitments and military decisions. The war expanded beyond Europe through colonial territories, naval warfare and campaigns in Africa, the Middle East and elsewhere. It mobilised entire societies and economies and became one of the first conflicts in which industrial technology was systematically combined with mass conscription on an enormous scale.
The immediate crisis of 1914 developed within an international system divided by alliances and strategic commitments. Germany and Austria Hungary were aligned with the Ottoman Empire and Bulgaria in the Central Powers, while Britain, France and Russia formed the principal Allied combination, later joined by Italy, the United States and other states. Alliance systems did not mechanically cause war, but they increased the potential consequences of decisions taken during the July Crisis.
Military mobilisation schedules also constrained governments because railway timetables and prewar plans assumed rapid deployment. Germany's decision to implement the Schlieffen based strategy involved invading Belgium in order to attack France, bringing Britain into the war. The crisis therefore escalated from a regional dispute into a major European conflict within weeks.
The First World War was characterised by industrialised mass warfare. Machine guns, rapid firing artillery, barbed wire and fortified positions made defensive fire extremely powerful, particularly on the Western Front. Artillery caused the majority of battlefield casualties and became central to attempts to destroy enemy positions before infantry attacks. Poison gas introduced another weapon, although conventional artillery remained far more important. Aircraft initially served mainly reconnaissance functions but increasingly became involved in artillery observation, bombing and air combat. Tanks appeared on the Western Front from 1916 as an attempt to overcome trench obstacles, though their early reliability and numbers were limited. Submarines transformed naval warfare by threatening merchant shipping and contributed to debates about unrestricted submarine warfare.
The war became a conflict of economic mobilisation as well as battlefield combat. Governments increasingly directed industrial production towards weapons, ammunition, uniforms, transport and food supply. Britain used its naval power to restrict German imports, while Germany faced severe shortages as the blockade continued. States borrowed enormous sums, introduced taxation and expanded administrative control over economies. Civilian populations experienced rationing, inflation, shortages and disruption of international trade.
Women entered occupations previously dominated by men because millions of men were serving in the armed forces, although women had already participated extensively in paid and unpaid economic activity. The war therefore expanded the administrative reach of governments and changed relationships between states, businesses and households.
The principal theatres included the Western Front in France and Belgium, the Eastern Front between Germany and Russia, the Balkans, the Italian Front, the Ottoman territories and several campaigns in Africa and the Middle East. The Gallipoli Campaign attempted to force the Dardanelles and open a route to Russia but failed. British and French forces fought Ottoman forces in Mesopotamia and Palestine, while Arab forces participated in the wider struggle against Ottoman authority. German and Ottoman colonies in Africa and the Pacific were also attacked. Naval warfare extended across the Atlantic and other oceans. The war was therefore genuinely global in geographical reach, although the largest concentration of industrial armies remained in Europe.
Russia's withdrawal was one of the major turning points of the war. Military failures, economic disruption and political crisis contributed to the Russian Revolutions of 1917. The Bolsheviks subsequently sought an end to the war and concluded the Treaty of Brest Litovsk with the Central Powers in March 1918, removing Russia from the conflict. Germany then transferred forces from the Eastern Front to the west and launched its major spring offensives in 1918. The United States had entered the war in April 1917, and increasing American personnel and material strengthened the Allied position. German offensives failed to achieve decisive victory, while Allied counteroffensives from August 1918 steadily weakened German forces.
The war ended through a series of military collapses and political transformations rather than through one single decisive battlefield event. Bulgaria, the Ottoman Empire and Austria Hungary left the conflict in late 1918, while Germany experienced revolution and the abdication of Kaiser Wilhelm II. The armistice on 11 November 1918 ended fighting on the Western Front. The subsequent peace settlement included the Treaty of Versailles with Germany and other treaties concerning the defeated Central Powers. The Austro Hungarian and Ottoman empires were dismantled, new states emerged and Germany lost territory and faced military and financial restrictions. The settlement created new international problems because borders, minority rights, reparations and national self determination were contested in many regions.
The consequences of the First World War extended far beyond 1918. Millions of soldiers and civilians died, while many more were wounded, displaced or traumatised. The war contributed to the collapse of several empires, the creation of new states, revolutionary movements and political instability. The League of Nations was established as an attempt to create an international system for collective security, although its effectiveness was limited by institutional weaknesses and the absence of sustained participation by some major powers.
Economic disruption and political radicalisation contributed to later instability, although the Second World War cannot be explained by the First World War alone. The conflict also changed military technology, public administration, social roles and cultural attitudes, making it one of the central turning points of twentieth century history.
