Immediately prior to world war i, an increase in nationalism and a complex system of alliances between major european powers created a tense situation. which single event sparked the beginning of the war? a. the sinking of the unarmed british passenger ship lusitania in 1915 b. the discovery of the zimmerman note by american diplomats in 1917 c. the unprovoked invasion of france by chancellor otto von bismarck in 1914 d. the assassination of archduke francis ferdinand by serbian radicals in 1914