Why do Americans seem mad that China invested in your nation and lent your government money?

Yeah, global economic policy really boils down to that, not. If you believe that, you are a fool. China keeps the value of their currency artificially low. China is not yours or anyone's friend other than their own. Chinese dominance of Asia only spells bad news for free peoples so long as they are run by an openly oppressive regime which will roll tanks over protesters.