The Second World War Marked the Most Substantial Change Ever

The Second World War marked the most substantial change ever in the context in which United States foreign policy is made. The world that emerged after the war had fundamentally changed in economic, political, and military ways. These changes made the world a more dangerous place, and altered the demands placed on foreign policy. The statement calls the world after the Second World War "a more dangerous place." What specific change could one cite to support this claim?

A) The rise of the European Union (EU)
B) The signing of the General Agreement on Trade and Tariffs (GATT)
C) The decline of German military power
D) The development and spread of nuclear weapons