President James Monroe asserts U.S. opposition to further European colonization in the Americas.

The U.S. enters World War I, playing a crucial role in the Allied victory.

The U.S. engages in a decades-long geopolitical rivalry with the Soviet Union, marked by proxy wars, espionage, and nuclear deterrence.

The U.S. responds to the 9/11 attacks by launching military operations in Afghanistan and Iraq, and engaging in global counterterrorism efforts.