system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is the USA allowed to have active military bases in other countries?

I feel like we would never allow another country to set up a military base in our soil, yet we have tons of military bases set up in foreign countries? Why is that ok for us but not them?
gpt
Usually it's because they sign treaties saying that we should be there. That's how it works. 

Sometimes it's because they want protection (a bunch of Eastern European countries want them), other times it's part of trade negotiations (Destroyers for Bases program), other times they were bought or leased (Cuba), other times it's a condition imposed upon countries as terms of their surrender (Japan). 

The reason other countries don't have bases here is because there's no point. Forcing us to allow bases obviously doesn't work, so that condition is out. Protection is also out, given that we're stronger than everyone else. Selling the land isn't something we need to do, not that it matters because no one else has the force projection to actually make use out of a base which is on the other side of the world. 

That said, we do do tons of joint training with foreign soldiers on American soil. It's a pretty regular thing.