First of all, there is more than the US. So let's not get into US centrism. I'm from Germany and we had issues with those ppl as well. The US alone would not have been able to stop this at all. Secondly, the endemic stage was guaranteed to happen in the very moment Covid left Wuhan province. That was the last time it was stoppable. Given it's incubation time, there was no way we could have caught all infected in time as soon as it left the very distinct borders it first occurred in.