The entangling alliances among the European powers affected World War I by causing a small regional conflict to explode into an international war. The first of the two major alliances in this war was the Central Powers dominated by Germany, Austria-Hungary and Turkey. Their opponents were the Allies made up of France, Great Britain, Russia, Japan, Italy and eventually the United States.
The war began with a relatively small incident, the June 28, 1914, assassination of the Austrian Archduke Franz Ferdinand and his wife in Sarajevo by Gavrilo Princip, a Bosnian Serb. Serbia disclaimed any responsibility for the attack. However, knowing that Serbia had designs on its territories in the Balkans, the government of Austria-Hungary suspected Serbia of complicity and eventually went on the attack. This attack caused a cascade of alliances to go into effect. Russia rushed to the support of its ally Serbia by mobilizing its troops. This caused Austria-Hungary and Germany to mobilize their troops against Russia. At this point, to defend its ally and attack its longtime enemy, Germany, France began to ready its troops. Germany attacked France through Belgium, a country whose neutrality Great Britain had sworn to defend. This act dragged the British military into the war. By September 1914, Japan and the Ottoman Turks had joined as well, creating a tangled conflict between the alliances that took place not only in Europe but also throughout the world, in the open sea, and in European colonies in Africa and Asia.