Which event started World War I? O A. the sinking of the Lusitania by German U-boats

OB. the assassination of Archduke Franz Ferdinand and his wife, Sophie

OC. Germany's annexation of Alsace and Lorraine after the Franco-Prussian War

D.

the Russian enforcement of Pan-Slavism throughout Slavic nations

E.

the signing of treaties in 1839 and 1867 to protect Belgium's neutrality

The assassination of Archduke Franz Ferdinand and his wife Sophie in Serajevo was the immediate cause of World War I.

Explanation:

There are many causes for the rise of the First World War like the rise of national sentiments, all the major European powers were colonizing abroad, their selfishness, spirit of aggrandizement increased to such an extent that they started bitter rivalries among themselves. William Kaiser II, the German Emperor cherished ambitions of world domination. In 1907, Europe was divided into two hostile camps. The chief causes were the secret alliances between England, France, Russia and Japan and on the other between Germany, Austria - Hungary, Turkey and Italy. The other causes such as compulsory military training, competition in creating destructive weapons, thirst for colonial expansion, ignoring of public opinion in the European Kingdoms. Austria always opposed Serbia in the Balkan Peninsula and the Serbs disliked the Austrians. Many times, Serbia had to accept terms of Austria which were unjust downright. There were prior reasons of estranged relationship between Austria and Serbia as well as among the European powers before the assassination and the assassination served as an immediate cause for their thirst which had led to a World War.