A significant expenditure for us, an overwhelming one for the other side, of money, arms, and conflict to destroy a region's viability therefore ensuring that any (including capitalism) economic system will fail. The aim is force people to either capitulate to us in the hope we will bring in re-construction money, or terrorize others into falling in line.

Read Chomsky, he'll give you references (from the likes of the declassified CIA documents, ect)

For example

Russian Civil War. That's well before they "ruled half the world's economy". Btw, the side we picked were real pricks. The only ones who could make the Bolsheviks the better alternative.

Greek civil war. Here we started sweeping away the commies (who actually liberated Greece) while we stil at war with the Nazis.

Cuba, nasty embargo. Numerous terrorist act committed by our proxies. The point here is to demonstrate to L. America the punishment of going red.

Cambodia. Bombed them to the stone age destroying all their capital. We were so through, people predicted that millions would die even if the Khmer Rouge hadn't (the predictions, btw, predate the Khmer Rouge taking power).

Cambodian side note: by the 1980s we were siding with the Khmer Rouge against Vietnam. Politics and bed fellows and all of that.

Vietnam. We dumped so much Agent Orange that they can't grow non-poisonous produce if they tried. We destroyed all their industrial capital.

N. Korea. We bombed them so throughly that we ran out of civilian* targets. We bombed them for things we hung Nazis for (irrigation damns). Needless to say they had no capital.

Read more Chomsky for more fun (and references) !

* Did you really mean economy or landmass, or population? I don't think the combined socialist countries, at their height in the late 70s, got close to third the world economy, nevermind half. To be clear, i don't expect socialism to work. I just don't get why we bomb those who try it.