How? It was on the opposite side: the Soviet Union (i.e. the USSR) and its "satellite" states (that is, smaller states which the Soviet Union forced into a common security/political/economic alliance) versus the West (the United States and Western Europe).. . During the Cold War, which lasted from 1945 to 1991, each side attempted to strengthen its alliances and to achieve nuclear superiority. Both the Soviet Union and the United States had nuclear weaponry that assured mutual destruction if the other side attempted to launch a first attack. The word "cold" from Cold War comes from the idea that unlike a "hot" war where the two sides directly confront each other with a full-out war, the Cold War was more about careful diplomacy and behind-the-scenes maneuvering. The US and the Soviet Union never directly confronted each other in a war, although American and Soviet (or Soviet-trained) troops would often clash in smaller wars, such as the Korean War and in VietNam.. . The Cold War was as much a war of imagery as a war of military strategy, because each side knew that nuclear weapons could not be used, and because even some conventional weapons could raise the threat that the other side would use a nuclear weapon. The closest either side came to all-out confrontation was in 1962, when American spy planes discovered that the Soviets had secretly installed missiles in Cuba, just 90 miles off the coast of the US. The Soviets eventually removed the missiles.. . During the Cold War both sides attempted to strengthen their position in poor Third World nations, largely because this was a testing ground for each side's superiority- and also because each additional "ally" on one side was less an ally for the other. These nations were not essential to either side winning the Cold War as much as they reinforced the image of superiority for either side and removed the perceived threat that one side might gradually spread its influence in neutral Third World territory. The US became involved in Viet Nam largely under the premise of the Domino Theory: if one nation falls into the Soviet communist sphere, many others will follow. This was also the basis for US involvement in Central and South America in the 1970s and 1980s. During the post-colonial era, Africa and the Middle East became important staging grounds for Soviet communist involvement under the false premise that this involvement was "requested" from abroad. (The Soviets had always claimed that they were anti-Imperialists, and that unlike the US they simply wanted to spread independence and good will. Of course, this is highly contrasted my direct military involvement in Eastern Europe after World War II and again in Hungary in 1956 and in Czechoslovakia in 1968. It is also contrasted with the Afghan War in the 1980s).. . In a sense, it would be a misnomer to claim that the Cold War was totally "cold". Billions of dollars were spent on defense during this time, and a number of smaller wars were fought. But neither side directly confronted the other on the battlefield and by the late 1980s the Soviet influence was waning (come would argue because the cost to the Soviets was much less bearable than it was to the US). In 1989 a succession of independence movements in Eastern Europe relinquished the Soviet Union's control over this important sphere. It was only a matter of time before the Soviet Union itself collapsed in 1991. A number of the republics of the USSR gained independence, the majority of which then formed a loose confederation of independent states with Russia. . . I hope this helps. If you would like to know about more specific events or aspects of the Cold War, try wikipedia.org. The shortest answer possible to your question is that they were the other side, what we sometimes refer to as the "bad guys" (of course that's totally relative to where you stand).