Among the Major Factors Leading to the Outbreak of War

Among the major factors leading to the outbreak of war in mid-1914 was

A) Nationalism and internal dissent.
B) German leaders' determination to end Danish opposition to construction of a huge naval base at Kiel.
C) Japan's determination to seize either United States or German colonies in the Pacific, leading to the Japanese declaration of war against Germany in mid-August 1914.
D) Russia's unexpected attack on Serbia and Bulgaria in late June 1914.
E) the assassination of the heir to the Russian Empire.