They came 20,000+ years ago.
That was at least 16,000 yeare before there was the first real “Chinese” state of the Xia dynasty. The Han people called themselves the Huaxia people around 2200 BC.
20k years ago, there was no China, no USA, no Chinese nor English nor even proto indo European language nor Tibet burmese language.
Bring back Pangea!
The also emigrated without permission from the Party, a big no-no.