World War I began on 28 July 1914 and lasted until 11 November 1918. The underlying cause of the war was a complex series of political, territorial and economic problems. The stage for war was set on June 1914 with the assassination of Archduke Franz Ferdinand of Austria. Within weeks, the major powers were at war, and the conflict quickly spread around the world. Initially the United Kingdom, France and the Russian Empire were fighting with the Central Powers of Germany and Austria-Hungary. Before long Italy and Japan joined the Allies while the Ottoman Empire and Bulgaria joined the Central Powers. By early 1915, the fighting had reached an impasse on the Western Front. Artillery barrages, along with water-cooled machine guns, made crossing open ground impossible. Massed infantry advances on enemy positions became suicidal. Armies had not developed infantry tactics for breaching entrenched positions without suffering heavy casualties. However, new offensive weapons, such as gas warfare and the tank designed to break the stalemate began to appear on the battle field.
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