Well, the usual trick since WWII is to put some dictator or otherwise US friendly government in place, sometimes with an invasion, sometimes by covert action or sponsorship of a select few. While actually putting a US governor (first citizen or whatever) and "police" force in place might be too much for US allies, this gets by for some part as long as it is not too obvious.

More directly: How about when we define colonization as "forcing another country to serve your countries needs"? Sounds reasonable? OK, then there are Iraq, Grenada, Guatemala, Nicaragua, El Salvador, Panama, Chili, Argentina. Oh, there are some notable failed attempts like Vietnam and Cuba.

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