1) Several factors led to the outbreak of World War 1 in 1914, including imperialism, nationalism, militarism, and a system of tightly bound European alliances. 2) When Archduke Franz Ferdinand of Austria-Hungary was assassinated by a Serbian nationalist, it prompted Austria-Hungary to declare war on Serbia and pulled the other European powers into war through their alliance systems. 3) The war quickly escalated as Germany declared war on Russia, France, and Belgium, drawing the other European powers into a massive four-year conflict fought across Europe, Africa, and at sea.