The Cold War was a period of political tension between the United States and their allies against the Soviet Union and their allies. In general, the period is considered to have lasted from 1947 to 1991. The term "Cold War" reflects the fact that there was not any "hot", direct, large-scale battles between the sides, but it was in essence a "war" because lives were lost, military power was increased, and each side attempted to dominate the other. In addition to the resources listed below, the collections of the American Heritage Center contains some unique primary source materials about the Cold War.