The assassination of Archduke Franz Ferdinand of Austria-Hungary in Sarajevo caused a chain reaction where the Austia-Hungarian goverment, who had annexed Bosnia fired off ultimatums at the Bosnian Slavs, as a Slav was responsible for the assassination. Because of old treaties and the fact that the majority of Russia was made up of Slavish people meant the Tsar placed an ultimatum on Austria-Hungary telling them to stop oppressing the Bosnian Slaves. When Austia-Hungary failed to stop, Russia declared war on them. But then because of a treaty with A-H germany declared war on Russia, then because of a series of other ultimatums, France became involved and was invaded by germany. An allience between France and Britain, and jealous rivalry of Germany because both countries were competing in an Arms Race, Britain became involved and declared war on germany. I think thats mostly correct. But standard grade history is a fuzzy memory now.