In the years before the war, the powers were forming military alliances to defend their objectives:

1. The Triple Alliance linking Germany with Austria-Hungary and Italy. It was signed in 1882, in the days of Chancellor Bismarck. The German Reich and the Austro-Hungarian Empire constituted the core of this alliance.

2. The Triple Entente, which was made up of Britain, France, and Russia, concluded by 1907. The increasing German aggression led to Britain and France ending their colonial differences. The rivalry between Austria-Hungary and Russia in the Balkans pushed Russia into the alliance.

During the decade before the war, four successive international crises marked the evolution toward a widespread conflict. Two took place in Morocco where Germany and France clashed. Two occurred in the Balkans, Russia and Austria-Hungary fought to replace Turkey as the hegemonic power.
The final crisis took place on June 28, 1914 when the Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, was assassinated in Sarajevo (Bosnia). An activist Bosnian Serb, Gavrilo Princip, a member of the Serbian nationalist organization "Black Hand" killed the Archduke. The alliances started working and it led from a local conflict to a general war in Europe and the world.