People forget that we shut down immigration for a few decades in the 1900s to let people assimilate.
We’ve overdone it, we need to slow the influx again.
We don't have a clear ratio of how many were born in the Americas, when Independence was proclaimed. I concede the majority was likely born on that soil. I find that irrelevant to the parent comment stating immigration was controlled in the early 1900s.
It was quota was set at 2% of each nationality's population as recorded in the 1890 census. That date is revealing.
The mass migration of Southern and Eastern Europeans, Italians, Jews, Slavs, etc happened after 1890. The act anchored the quota to 1890, Congress deliberately set the baseline before those groups arrived in large numbers.
The result: nations with large post-1890 diasporas, and of course all of Asia and Africa, got tiny quotas, while Northern and Western European nations got huge ones.
I don't call this stopping immigration. Rather codified national selection. It may have helped with "assimilation". But no one can deny the maneuver was for national discrimination.