There are plenty of folks who came over after the bulk of the genocide was largely done. Don’t think an Italian coming over in the 1910s had fuck all to do with the Native American genocide.

The US did not stop at that genocide.

But even ignoring that you are assuming that this is all a black and white situation when people are rarely that. For example the early Scots-Irish population in Appalachia generally got along well enough with native Americans often times even mixing together, you could also have the later Irish immigrants from the Irish genocide by the English inflicting the same fate apon Native Americans in the great planes.

And yet, what the (pre-)USians were doing was still predominantly a settler-colonial genocide, regardless of whether there were a few nice exceptions.