In World War I, Russia was allied with the British Empire and French Republic and therefore fought on the same side as America. In World War II, Russia, now known as the Soviet Union, signed a non-aggression pact with Germany in 1939, in which this pact, was broken by Germany in 1941, so by the time America joined this World War, the Soviet Union, was now aligned with the Allies, and consequently as in World War I, the Soviet Union and the United States of America fought on the same side. At the conclusion of World War II, there was only one country in the world that had master the usage of the incredibly destructive atomic power, which was America, but that was to change in 1949, when the Soviet Union, joined that exclusive club. Additionally, it was not till the conflict in Korea, that the Soviet Union, first opposed the United States in battle, though the Soviet Union essentially did so in logistical and war material support of the Chinese on behalf of the North Koreans.
In 1991, the Soviet Union, relinquished its control of its sister empires, and once again, became Russia, to which there were many reasons why this occurred, of which, the most important would be that even when countries such as the Ukraine and Uzbekistan were part of the USSR, they had never been fully absorbed into the Soviet Union, proper, that is to say they were typically treated as satellites to the power of Moscow, with typically different ethnic identities, different historical religious identification, and repeated failures of economic and growth planning, In addition, to all of that, Russia itself, is nearly twice the physical size of the next biggest country in the world, so that controlling or aligning itself with other nations under the soviet empire, was done more for the protection and as a buffer for Russian territory, which previously had been attacked by Napoleon as well as Germany.
How united the Soviet Union was at its peak, is very debatable, so that, at best, the countries of the Soviet Union basically equaled the population of the United States, during the era of 1950-1990, however, if one was to add onto the population of America, all of the nations aligned with America in NATO, during the same era of 1950-1990, the size of the population of NATO along with its military muscle and firepower, even at the Soviet Union's peak, would clearly have significantly favored NATO. This would signify that all of the military buildup, all of the military posturing that was done repeatedly and is, to a lesser extent, still done today in regards to Russia and how menacing Russia is, or how dangerous communism is, and so on and so forth, was in essence, an overreaction to the fact that Russia had atomic weapons, and the United States was deeply troubled by that, because atomic weapons have the clear ability to end life as we know it on this planet.
To put things in present-day perspective though, Russia's population in 2010 was about 143 million peoples, whereas America's population was about 309 million peoples, and as reported by the International Monetary Fund the GDP of the United States of America for 2016 was the highest in the world at $18.569 billion dollars, whereas Russia was not even in the top ten, with only $1.28 billion dollars, which is less GDP than Canada or even South Korea. This then, is the basic proof that Russia, or the former Soviet Union, was never the menace or danger that it was made out to be, and that with the exception of satisfying the military-industrial complex and certain political elements that have a fixation on seeing a "boogeyman" there isn't any reason to fear Russia whatsoever, today. In fact, Russia, wants to be our friend, which historically, more often than not, it has been, in which Russia was either sympathetic to our side as it was to the North in our civil war, or as a neutral which it was in our revolutionary war, or fought by our side as it did valiantly in the two World Wars.