Tension had been rising between the European powers for many years. The events that took place in Sarajevo in 1914, unleashed a series of events that finally lighted a fuse which would explode into the First World War. The key event, which started this chain reaction was the assassination of the Archduke Franz Ferdinand, who was the heir to the throne of the Austro-Hungarian Empire.hope that answered your question :) have a nice day :)