In the social sciences, theories won’t get us very far. Instead, we should look at the economic systems, e.g., USSR, CPR, Egypt, Great Britain, and the thousands of small communist and anarchist utopias around the world throughout history. There we will find that all communist economies eventually floundered because of lack of monetary incentives. They reduced the lowest levels of poverty, but could not advance the general material welfare. Internal violence was reduced, but not necessarily international violence. The only societies that had successful communist economies were primitive native tribes, e.g., American Indians, where most goods were owned by the tribe and personal possessions were few.
It is true, democracies, autocracies, etc., are forms of government that have little connection with economic welfare. To understand that subject, we have to look at the economic systems, e.g., capitalism, socialism, communism, etc. Any of the above governments can and have worked with these different economic models with success (and failure). To date, capitalism has shown better results than any other system. However, the current forms of western capitalism are heavily modified by government “rules of the game” that ameliorate the unfavorable side-effects, such as, depressions, excessive inequality, poverty, etc.
Furthermore, feudal, socialist, and communist economies all over the globe, from small utopias (New Harmony, Lanark, Oneida in the U.S.) to colossal nations (Russia), with very few exceptions, have given up on their attempts to establish egalitarian societies because equality and incentive are incompatible.
Where they failed, leftists and fascists removed these governments, but ultimately failed to provide an adequate prescription for per capita income advancement, either by improving technologies or conquering other countries, or both. They are mostly obsolete today. Additionally, all attempts by leftist governments to create classless societies, resulted in merely replacing the capitalist classes with bureaucratic classes, the general population remaining as poor as ever.
The capitalist countries certainly have no incentive to lend money to leftist governments as a matter of ideology. The best that a new Marxist government can do is redistribute income from the rich to the poor as was done in revolutionary Russia, and Cuba, but then what?
Inexorably, the lack of incentives under socialism, communism, or any other leftist brand will lead to malaise and poverty. There are ample lessons in the 75 years of wars to reach the simple conclusion that democratic socialist nations are not successful.