The nation primarily involved in the Cold War with the United States was the Soviet Union. This conflict began after World War II and characterized the geopolitical tension between Western capitalist democracies, led by the U.S., and Eastern communist states, dominated by the Soviet Union. The Cold War involved political, military, and ideological struggles, leading to significant events like the Cuban Missile Crisis and the Korean War. It also resulted in a nuclear arms race and competing spheres of influence globally. The ideological clash between capitalism and communism influenced international relations for decades, shaping the course of history through various proxy wars and diplomatic negotiations.