But seriously, why didn't communism triumph in the 20th century when things were looking so good? If the russian revolution and chinese revolution can succeed, liberating 800 million people, 1/3rd of the world's population, defeat the nazis, why couldnt we finish the final stretch? What was the fatal flaw?
Well, there's a lot of commentary and debate about why the USSR failed, but communism is hardly dead in the water. A very substantial portion of the world's population lives in a socialist state - the PRC is the largest and soon the most powerful country in the world. Vietnam is a major player in Asia with a huge population. Cuba's kicking and stable. There's other smaller ones as well, and we're just talking ML countries. Socialism's having a moment in Latin America. Liberal capitalist countries are flailing internally and in their capacity to exert power globally.
So... Communism is still on the path to victory even with it's greatest champion fallen thirty years ago.
the question is why did the soviet union dissolve, and why communism did not triumph in the 20th century. I'd say we are perhaps past the nadir of the 90s where communism genuinely seemed over, but the reality is simply the failures in the 20th century did set back the global communist movement back massively.
Rome wasn’t build in a day. Capitalism, feudalism, and any other mode of production all took time to develop and then take hold. If you say the first socialist state is the Paris commune, this movement has been around for about 150 years. (It was also fucking dead in the water for decades after the commune’s failure.)
Although history moves faster these days, it’s a little like asking why it took hundreds of years for Rome to dominate the Mediterranean, why it took hundreds of years for landlords to make Europe feudal, why it took centuries for British capital to transform the world. These different modes of production are objectively real. Capitalism objectively produces a shitload of capital. Socialism takes that capital to the next fucking level, as China is beginning to show. Marx was initially wrong (it seems) when he predicted that the first revolutions would occur where capital was most developed; the 20th century shows that it’s much easier to organize the global south against imperialism than it is to organize the global north against capitalism (especially when so many of the global north’s workers are bribed by treats produced by slave labor in the global south). But maybe the 21st century will see the first successful revolutions in the imperial core, after which it’s game over for capitalism.