Where does “アメリカ人” come from?
アメリカ人 (Japanese) comes from Japanese アメリカ, from English America, from Latin America, from Italian Amerigo, from Proto-Germanic *Amalarīks, from Proto-Germanic Haimarīks, from Proto-Germanic rīks, from Proto-Celtic rīxs — to straighten, to right oneself; right; just.
アメリカ人 (Japanese): American person
Ancestry of “アメリカ人”, step by step