In exchange, the US gets the opportunity to set up military bases or to use their allies's military bases. And once you're there, you're staying and it becomes impossible to evict you*. And your allies have to deal with the consequences of the stupid wars you started. Mass immigration fuelling the rise of right-wing ideology in Europa is ultimately due to ongoing US meddling in the Middle East. Where is the free ride???

* Best example: Guantanamo Bay, which Cuba wants back and for which only a single rent check was (accidentally) deposited since the revolution.