What spark started world war 1 by setting off the power keg of nationalism that has been building in Europe in the period prior to 1914? A. the unplanned explosion at an armory in the Bosnian capital of Sarajevo B.The assassination of King Albert I of Belgium during an Austrian excursion C.The inadvertent firing of shots by a Serbian soldier on German troops D.The assassination of Archduke Franz Ferdinand of Austria.