By the time the US was truly becoming a nation in the 19th century there were multiple different European populations and some even caused strife within the US like the Irish and Italians. Hell people even briefly disliked the Germans during WW1.stop this meme. read history.
Unless you are about to sit there and tell me that Europeans are a homogeneous people and culture then the US has always been a diverse nation.
Very few empires/nations in history can claim to be as diverse as the US and usually when it came to empires it's because said empires conquered many different peoples.