What prevents the USA from gaining land from other countries? Can land be bought from another country for colonization under US protection?
There is nothing that makes this ontologically impossible. Politically, however, good opportunities are few, and the USA probably wouldn't be interested. Good opportunities to acquire land are few because:
- In lands where people live, governments may not be able to follow through on the sale. They represent their people but don't own them. The government might cash the check and then the voters might toss them out and refuse to hand themselves over to the USA.
- Public lands and wilderness could be purchased, but the US already has many tracts of wilderness land in the West which it could open up if there was really a large number of people who wanted to homestead there.
- It would be hard to imagine any return on the money. If we bought, say, a Canadian province, we could collect taxes from the residents but would also have to provide services, a break-even situation in the long run. So how would the purchase pay back the price?
But let's say a good opportunity came up, for example, to purchase the Panama Canal. Some of the reasons the USA might not be interested include:
- It would have to dispose of the residents. Displacing them is distasteful. Making them US citizens would be a political non-starter because they would likely side with one party, and the other party would block the deal. And keeping a permanent non-citizen underclass would be impractical for a whole array of reasons.
- Most of the attractive real estate is already privately owned, so there's no benefit to current US citizens (as individuals) for the purchase. It couldn't be "settled" and private citizens couldn't simply stake claims on valuable real estate. If they wanted to move there they'd have to buy a house from its current owner. Real estate prices might actually increase if the USA took over.
- Most of the benefits of that land could be acquired much more simply for money without taking on all of the problems. If Americans want to use the Panama Canal it's a lot simpler to just pay the Panamanians for the privilege.