You may be interested to learn that American immigration flows were higher or lower at various times (nearly zero for long periods). As you allude to with Native Americans, the effects of the different flows were not uniform on all people, and instead caused various negative and positive effects. The period of Americans great post-WWII economic and military rise came during its longest period of immigration moratorium, during which its population was fairly homogeneous. In recent decades, America has begun to decline economically and militarily relative to China, a country not subject to these "strengthening flows". Odd case.