I disagree with everyone so far. Lets be reasonable:
1) If the key to power is merely military spending, then France and the UK would easily have been too powerful for Moscow(i.e. the actual entity behind the Russian Empire, USSR, and the Russian Federation) to be able to challenge their hegemony. Even when you consider the war fatigue of the Second World War, it'd have been very easy to just arm more minor powers and even the somewhat neutral ones to take down the USSR which was even more war fatigued than everyone except Germany. Also, if military might was the independent variable, then game theory alone suggests that everyone would seek it and only highly militaristic countries could thrive.
2) On the economic system debate(communism vs capitalism), the idea of implying that an economic system defines a country is mostly false. Its the other way around and for a number of reasons. For instance, during the 20th century, The United States, Great Britain, and the various Commonwealth states throughout the world all had poor people, communists, and "national socialists" within their societies who, in turn, often had great influence in the shaping of the views of Communist and Nazis in mainland Europe. The 2 key differences between the UK/USA/Commonwealth group and mainland Europe were their legal systems(Common Law as opposed to Civil/Socialist law) and the fact that they were very resistant to the radical movements of Europe. Even Common Law India, despite a history of good relations with Moscow, never really embraced communism. Another issue with the "communism vs capitalism" argument is that both the USA and the Soviet Union started the 20th century being both geopolitically irrelevant(in the Old World) and opposite in their systems yet, by the 1950s, 60s, and 70s, both were more powerful than anyone else on earth. If the economic system was the deciding factor, then Moscow would've either been irrelevant or would have conquered the world.
3) A third key point to remember is that people often over simplify or miss-attribute the reasons for the success and failures of various empires in order to justify their own views or protect their own egos. Cognitive dissonance alone seriously clouds our understanding of why things occur the way they do since we don't want our ideals challenged and, even more so, we don't want our deeply-held beliefs to be revealed to be products of our condition rather than choice. For instance: Rome didn't fall because of Christianity or lead in their aqueducts(the Eastern half had both, was more religious, and lasted till the 1453); Nazi Germany wasn't powerful because of Hitler and his ideas but instead because, for the first time, there was a unified German nation-state(which, in turn, due to the presence of ethnically non-German people coupled with the German nation trying to define itself, led to both the Holocaust and the obsession with eugenics); and lastly, the United States is not the most powerful nation on earth because of freedom, the aftermath of WW2, or any anti-American conspiracy theories but rather because of its political decentralization, its use of Common Law augmented by a Bill of Rights, and its civic, rather than ethnic, national identity due to the combined effects diseases and war killing off the indigenous population and the new population being made up of immigrants who's descendents became too mixed to be caught up in Old-World conflicts and, lastly, because of its relative isolation from the affairs of the Old World. When you try to re-write history so it matches your political/religious views, then you end up adopting a distorted worldview that dissuades you from trying to understand why it is the way it is.
Here's why Moscow's empire(s) became so strong during the 20th century and why the arguments that try to downplay or explain that due to [insert things related to store shelves or tanks] miss the point:
1) The land surrounding Moscow that we refer to as "Russia" or, during the Cold War, as the "Soviet Union", is actually owned and economically dominated by Moscow. Whereas in the "West" we're used to political capitals who have to derive their authority from the consent of economic/political rivals in the various federated states or, as in unitary states, from the various population centers, in Russia its quite the opposite and even Google Earth can show you how. While Western states derive their economic power from trade and their military power from alliances(2 things which require freer societies) and thus benefit from their governments refraining from trying to centralize too much power, in Russia, however, Moscow is overtly centralized within the network roads, rails, and, almost certainly, air lines within Russia. While this was done during its imperial days under the tsars in order to remain in control, such a layout today within a greatly multinational empire(yes, it technically still is) has the dual effects of keeping the capital centralized economically, even when doing so is wasteful, and also it has the effect of preventing regional development and thus the industrial and technological benefits that light and medium industry bring. This layout is thus the main reason the Soviet Union was so good at producing large numbers of rockets, missiles, tanks, and nukes (all products of heavy industry that benefit from central planning) while being unable to build decent consumer goods, automobiles, consumer electronics, or anything else that, in layman's terms, "had a lot of small parts that came from many different areas". Just imagine trying to build or improve any complex gadget in a country where logistics are a nightmare due to a transportation infrastructure designed primarily to connect cities and towns to the capital, where there's no Interstate Highway System to fuel the growth of light and medium industry on beltways which are essential for regional internal trade which is, in turn, essential for complex and rapidly-changing modern technology, and where there is no cheap land to build new factories despite all the undeveloped real estate that encircles virtually every city but is inaccessible. USSR could build missiles, tanks, and spacecrafts easily since those are big items that are easier to produce when the government ensures that they have priority when it comes to logistics, location, and investment. This is why the argument that the USSR was dirt poor but had a strong military is false: they were clearly able to coordinate simple and essential resources well but they focused on military hardware because they could make tanks more efficiently than cars and stoves.
2) Like the United States, Russia entered the 20th century as a relatively weak power with an inward focus. Both countries avoided getting involved in European politics and conflicts with great powers. Russian society wasn't very open to the outside world but revolutionary ideas did tend to seep in and were exacerbated by economic problems and military defeat with Japan. When the First World War occurred, Russia suffered greatly and went into a revolution which replaced the regime. America played a smaller role in the war, was by allied powers, and paid a financial price for getting involved. When the USSR rose to power, pretty much the whole structure of Russian society was changed since suddenly everything that would have gotten in the way of rapid industrialization was either killed or fled. This meant that the young USSR, much like the United States not long before, didn't have to work within a system that preferred the status quo and thus could greatly expand its power without facing either internal resistance(aristocrats/nobles) or external resistance(Europe using various means to either weaken Russia or use Russia's new growth as an investment opportunity which would, in turn, dampen expansion due to efforts to bring about more stability). Essentially, Russia was able to wipe the slate clean without lingering interests slowing it down.
3) Russian economic strength was in mass production of simple military goods. This gave them the ability to protect and hold large amounts of land within eastern Europe. Considering how uncompetitive the Soviet market was, the use of force to tie other countries to Moscow enabled the USSR to survive better than an equivalent country that engaged in free trade with the United States. While this strategy tended to work, there was only so much growth that could occur until the economy started to slow down due to the inefficient system and increasing bureaucracy overtaking the gains that they had during the early days and after WW2. Simply put, the Soviet Union failed because because the resource it relied upon - human labor - was less and less available.