Or, rather, it was the dialectic of nation against empire that once made Marxism popular. Marxism used to be the dominant ideology of resistance because Marxists often aided, and they sometimes led, national liberation movements. That's the main reason -- perhaps the only reason -- for its popularity in the early to mid 20th century.
That is also the reason why Marxism never became very popular in countries where capitalism has been the strongest, for such countries have been imperial powers themselves, (now integrated into one multinational empire under US leadership), so their peoples have never had to look for a powerful political tool that would serve as an effective weapon to fight against capitalist imperialism.
State socialism did not build foundations for communist society.
However, if nothing else, it often succeeded in driving countries in which it became hegemonic through transition from semi-feudal social formations, many of them dominated by empires, to modern nations, albeit at great costs to populaces under it. I do not believe that the costs of transition would have been lower if the driving force had been capitalism rather than state socialism (compare China with India, the latter is still semi-feudal in the countryside, with low rates of literacy and high rates of malnutrition among the poor), and moreover, you can readily see what becomes of people who fail to make that transition, which empires obstructed, by looking at Afghanistan.
The political currents on the Left that prioritized local class struggles over national struggles, such as anarchism, council communism, Trotskyism, and so on, did not find comparable mass support worldwide, for their ideas did not resonate with colonial and neo-colonial subjects fighting against imperial masters.
Will things be different in the 21st century? So far, there is no sign that they will be. The most successful current of leftists in the world today, Hugo Chavez and his supporters, are anti-imperialist patriots first and foremost.
Historical materialists will make contributions to struggle to the extent that we can make ourselves useful to people struggling for republican democracy, against US hegemony. -- Yoshie