World War 1, also known as the Great War, involved two main sides - the Allied Powers including Britain, France, Russia, Japan, and the United States, and the Central Powers consisting of Germany, the Ottoman Empire, and the Austro-Hungarian Empire. The main reasons for the war included militarism, formation of alliances through treaties, imperialism, and nationalism. The immediate cause was the assassination of Archduke Franz Ferdinand of Austria-Hungary in June 1914 by a Serbian nationalist terrorist, leading to Austria-Hungary declaring war on Serbia. This triggered a chain of alliances with Serbia and Russia on one side, and Germany and Austria-Hungary on the other, culminating in the start of World War 1 on July 28, 1914. The war escalated with Germany declaring war on France and Great Britain. Russia was eventually tricked into war by Germany's claim of an attack by the Ottoman Empire.