I suggest you look at a map of the US in 1776 and compare it to today it's quite significantly larger now, imagine if today that 80% wasn't part of the US, an

I suggest you look at a map of the US in 1776 and compare it to today it's quite significantly larger now, imagine if today that 80% wasn't part of the US, and was instead controlled by the indigenous population (likely tens of sovereign states) would there have been large scale wars in the 19th and 20th century? it's quite obvious the answer would have been "yes"