Imo the flaw of both the op and this comment is it almost completely leaves out the reasons why it is “young”. Were the people who created the “new” culture settling on pristine virgin land? What could possibly have happened to the existing people who bore the “old” culture? Hmm

spoiler: the answer is that anglo saxon protestants were convinced of their superiority and almost uniquely violent, with few qualms about outright massacring and displacing natives. At least the spanish speaking catholics in south america intermarried and assimilated somewhat