What Turned the Political Assassination of Franz Ferdinand into a Worldwide

What turned the political assassination of Franz Ferdinand into a worldwide event involving all of the Great Powers was

A) competition among industrialized nations.
B) the preexisting system of alliances triggered a chain of events beyond political control.
C) the familial squabbles of the royal houses of Europe, all grandchildren of Queen Victoria.
D) the opportunity to incite revolution in China and Russia.
E) the entry of the United States into the fray of war.