I'm no expert, but anecdotally I can tell that the idea that the oaths are holdovers doesn't quite apply to the US. Their oath is worded in such a way that you

I'm no expert, but anecdotally I can tell that the idea that the oaths are holdovers doesn't quite apply to the US. Their oath is worded in such a way that you very clearly have to give up loyalty to any other country state, but the US was never governed by a single monarch/ruler (after independence of course).