This signaled the end of the Cold War between the Soviet Union and the United States. Learn about the Soviet invasion of Afghanistan and the roles of Gorbachev and Reagan. The collapse of the Soviet Union started in the late 1980s and was complete when the country broke up into 15 independent states on December 25, 1991. Mikhail Gorbachev Becomes General Secretary For Higher History, revise the reasons for the end of the Cold War. After the collapse of the Soviet Union in the year 1991 that finished the Cold War, the post-cold War world was off and on again thought to be a unipolar world, with the United States as the world’s sole remaining superpower. The period occurred between 1947, the year of the Truman Doctrine, and 1991, when the Soviet Union collapsed. The Cold War was a geopolitical chess match between the United States, the Soviet Union, and both parties’ allies in which the major power players sought to project their respective ideologies across the globe in the wake of colonialism’s collapse following World War Two. Two important elements of power that lead to the collapse of the Soviet Union was military power and GDP. The realist explanation of the end of the Cold War and the collapse of the Soviet Union can be described in terms of power. The logic of power suggest that that in wars, the more powerful state will generally prevail.