The Great War was caused by militarism, alliances, nationalism, and imperialism, which ultimately led to the assassination of Archduke Franz Ferdinand and the outbreak of World War 1. Germany had begun building up its military, causing other European nations to feel threatened. The system of alliances pulled countries into the war - Germany and Austria-Hungary were allied, as were Russia and Serbia, and Russia and France. Serbian nationalism led to the assassination of Archduke Ferdinand by a Serbian nationalist group. This caused Austria to declare war on Serbia and triggered the chain of alliances that led to a widespread European war.