Britain also spent a long time transporting violent criminals and resettling much of the relatively violent “Scotch-Irish”/“Borderer” population to the American colonies. We also got a lot of their religious fanatics. This explains a lot about America.
If you're looking for ethnic explanations, the evidence deosnt match the claim that Borderers drive the American homicide rate to any real degree. While the White American murder rate is higher than Britain's, it's less than half that of the overall American murder rate, which is largely driven by the homicide rate amongst African Americans, which is 7x that of whites.
