the "American" ethnicity is a mixture of the Northwestern European ethnicities.
http://www.autoadmit.com/thread.php?thread_id=3448150&forum_id=2#48872593
http://www.xoxohth.com/thread.php?thread_id=3078072&mc=15&forum_id=2(http://www.autoadmit.com/thread.php?thread_id=1859275&forum_id=2:#49050693)