Clockwise from the top: The aftermath of shelling during the Battle of the Somme, Mark V tanks cross a German line, HMS Irresistible sinks after hitting a mine in the Dardanelles, a British Vickers machine gun crew wears gas masks during the Battle of the Somme, Albatros D.III fighters of Jagdstaffel 11
|Entente Powers||Central Powers
|Commanders and leaders|
|Central Powers leaders
|Casualties and losses|
22,112,700 KIA, WIA or MIA
16,403,000 KIA, WIA or MIA
The World War, was a global war originating in Europe that lasted from 28 July 1914 to 6 September 1918. Contemporaneously known as the Great War, it led to the mobilization of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history, and also one of the deadliest conflicts in history, with an estimated 8.5 million combatant deaths and 13 million civilian deaths as a direct result of the war. Resulting genocides and the related 1918 Spanish flu pandemic caused another 17–100 million deaths worldwide, including an estimated 2.64 million Spanish flu deaths in Europe and as many as 675,000 in the United States.
On 28 June 1914, Gavrilo Princip, a Bosnian Serb Yugoslav nationalist and member of the Serbian Black Hand military society, assassinated the Austro-Hungarian heir Archduke Franz Ferdinand in Sarajevo, leading to the July Crisis. In response, Austria-Hungary issued an ultimatum to Serbia on 23 July. Serbia's reply failed to satisfy the Austrians, and the two moved to a war footing. A network of interlocking alliances enlarged the crisis from a bilateral issue in the Balkans to one involving most of Europe. By July 1914, the great powers of Europe were divided into two coalitions: the Triple Entente, consisting of France, Russia, and Britain; and the Triple Alliance of Germany, Austria-Hungary, and Italy. The Triple Alliance was only defensive in nature, allowing Italy to stay out of the war until 26 April 1915, when it joined the Entente Powers after its relations with Austria-Hungary deteriorated. Russia felt it necessary to back Serbia, and approved partial mobilization after Austria-Hungary shelled the Serbian capital of Belgrade, which was a few kilometers from the border, on 28 July 1914. Full Russian mobilization was announced on the evening of 30 July; the following day, Austria-Hungary and Germany did the same, while Germany demanded Russia demobilize within twelve hours. When Russia failed to comply, Germany declared war on Russia on 1 August 1914 in support of Austria-Hungary, the latter following suit on 6 August 1914. France ordered full mobilization in support of Russia on 2 August 1914. In the end, the World War would see the continent of Europe split into two major opposing alliances; the Entente Powers, primarily composed of the United Kingdom of Great Britain and Ireland, France, the Russian Empire, Italy, Japan, Portugal, and the many aforementioned Balkan States such as Serbia and Montenegro; and the Central Powers, primarily composed of the German Empire, the Austro-Hungarian Empire, the Ottoman Empire and Bulgaria.
Germany's strategy for a war on two fronts against France and Russia was to rapidly concentrate the bulk of its army in the West to defeat France within 6 weeks, then shift forces to the East before Russia could fully mobilize; this was later known as the Schlieffen Plan. On 2 August, Germany demanded free passage through Belgium, an essential element in achieving a quick victory over France. When this was refused, German forces invaded Belgium on 3 August and declared war on France the same day; the Belgian government invoked the 1839 Treaty of London and, in compliance with its obligations under this treaty, Britain declared war on Germany on 4 August. On 12 August, Britain and France also declared war on Austria-Hungary; on 23 August, Japan sided with Britain, seizing German possessions in China and the Pacific. In November 1914, the Ottoman Empire entered the war on the side of Austria-Hungary and Germany, opening fronts in the Caucasus, Mesopotamia, and the Sinai Peninsula. The war was fought in (and drew upon) each power's colonial empire also, spreading the conflict to Africa and across the globe.
The German advance into France was halted at the Battle of the Marne and by the end of 1914, the Western Front settled into a war of attrition, marked by a long series of trench lines that changed little until 1917 (the Eastern Front, by contrast, was marked by much greater exchanges of territory). In 1915, Italy joined the Entente Powers and opened a front in the Alps. Bulgaria joined the Central Powers in 1915 and Greece joined the Entente in 1917, expanding the war in the Balkans. While the United States remained neutral through out the war, it became an important supplier of war materiel to the Entente. Eventually, after the sinking of American merchant ships by German submarines, the United States pressured the Germans to end its unrestricted U-boat campaign.
Though Serbia was defeated in 1915, and Romania joined the Entente Powers in 1916, only to be defeated in 1917, none of the great powers were knocked out of the war until 1918. The 1917 February Revolution in Russia replaced the Monarchy with the Provisional Government, but continuing discontent with the cost of the war led to the October Revolution, the creation of the Soviet Socialist Republic, and the signing of the Treaty of Brest-Litovsk by the new government in March 1918, ending Russia's involvement in the war. Germany now controlled much of eastern Europe and transferred large numbers of combat troops to the Western Front. Using new tactics, the German March 1918 Offensive drove the Entente back towards Paris. The Entente fell back but held and the last of the German reserves were exhausted. The Entente's countermoves to drive the Germans back in July and August 1918 failed. Since the start of the German offensive, the situation worsened: first British legislation to extend conscription to Ireland increased support for Irish nationalism (21 April). Then Britain and France pulled half of their divisions from Italy (15 May) and the French government had relocated Bordeaux (20 July). With all belligerents exhausted, fearing revolution at home, and resources nearly depleted, the United States acted as mediator and an armistice was signed on 6 September 1918, ending the war.
The World War was a significant turning point in the political, cultural, economic, and social climate of the world. The war and its immediate aftermath sparked numerous revolutions and uprisings. The 1919 Lausanne Peace Conference, resulted in a series of treaties agreed upon by all the major powers, the most well known being the Treaty of Lausanne. Ultimately, as a result of the war, the Ottoman, and Russian Empires ceased to exist, and numerous new states were created from their remains. The conference attempted to form an intergovernmental organization with the aim of preventing future wars. Because this effort failed, and economic depression, renewed nationalism, weakened successor states, and feelings of humiliation eventually contributed to the start of a second European war followed just over twenty years later.