The Cold War was significant because it dominated international relations and even had a tremendous impact on the domestic conditions in many countries from the end of WWII until the late 1980s. During that time, essentially everything that happened internationally was caused by or at least affected by the competition between the US and the USSR. In addition, many countries’ domestic politics and conditions were impacted. For example, the Cold War brought about McCarthyism in the US. It also helped cause the severe repression that existed in communist countries. Nothing was more significant in the last half of the 20th century than the Cold War.