Kings and Dictatorships are the most efficient and productive ASSUMING you have a good ruler in place. Two issues typically come up: finding the right person for the job and making sure people obey them instead of getting stabby.
Democracies and Senates are the most fair and keep everyone happy, but they're slow as Hell. They're also so watered down and full of so many differing views that ultimately no one is pissed or unhappy, they just sorta get by. And God Help you if a war gets fired up or a foreign nation starts talking crap, because they're just going to debate it while everyone is getting killed.
Communism and Socialism work once you have the infrastructure to support it. In the case of Russia, you kinda had the idea going without the factories and farms to support it. The problem is that once you install the system, people stop really developing and trying to progress. They don't make anymore money, so why bother to innovate or create things that aren't ordered by the government?
So they all have their ups and downs. America is a merger between a dictatorship and a Senate with a smattering of socialism. Unfortunately, the free market is mostly turning out to be a crock of garbage. Capitalism, as Marx said it would, does not breed innovation. One of the prime reasons for the economic collapse is that investors stopped doing anything risky and invested all their money in something as stupid as debt and interest. Sure, it made money, but a f***ing ten year old could have figured out that this can't last in the long run.
So, to conclude this rant, they're probably going to figure out a way to make capitalism run perpetually or just adopt a nationalized form of capitalism like China. Either way, I recommend learning to be productive in the near future.
