Not many ancestrally native Americans in Europe, relatively few jews compared to the USA (but more other semetic groups, I don't know if that balances or not), the sub-saharan Africans in Europe had a lot more volunteers and less industrialised human trafficing and are in any case very much more diverse genetically than people think due to superficial characteristics like skin colour (seriously, substitute race discussion about skin to be about blonde vs brunette to see how silly the groups are), and there's more of Irish in the US than the current population of Ireland.
Probably loads of other differences too.