If there was any slight difference between Americans and the other allied peoples during the war, Japanese called Americans Ameko like Americans called Japanese Jap. Rosuke for Russians and Chankoro for Chinese but there were no specific such insulting terms for the rest of them who were categorized as Keto (slang for people who have brown hairs). In the post war, I remember Japanese frequently used Keto like "Keto dropped atomic bombs" as Keto was represented by Americans.