Austria-Hungary declared war on Serbia for presumably harboring the terrorist
organization which assassinated Archduke Franz Ferdinand. Germany backed her
ally Austria to the limit, Russia mobilized in the hope of protecting her small ally, and
Germany declared war on Russia and on France, Russia's ally. German armies
crashed through neutral Belgium to crush France; and Britain, honoring her pledge to
defend Belgian neutrality, declared war on Germany
- excerpt from American Pageant, 3rd edition
Which of the following causes of World War I is being discussed in the excerpt above?
O imperialism
Onationalism
Omilitarism
O alliance system