World War I, military conflict, from 1914 to 1918, that began as a local European war between Austria-Hungary and Serbia on July 28, 1914; was transformed into a general European struggle by Germany's declaration of war against Russia on August 1, 1914; and eventually became a global war involving 32 nations. Twenty-eight of these nations, known as the Allies and the Associated Powers, and including Great Britain, France, Russia, Italy, and the United States, opposed the coalition known as the Central Powers, consisting of Germany, Austria-Hungary, Turkey, and Bulgaria. The immediate cause of the war between Austria-Hungary and Serbia was the assassination on June 28, 1914, at Sarajevo in Bosnia (then part of the Austro-Hungarian Empire; now in Bosnia and Herzegovina), of Archduke Francis Ferdinand, heir-presumptive to the Austrian and Hungarian thrones, by Gavrilo Princip, a Serb nationalist. The fundamental causes of the conflict, however, were rooted deeply in the European history of the previous century, particularly in the political and economic policies that prevailed on the Continent after 1871, the year that marked the emergence of Germany as a great world power.