Comment by AlotOfReading

As far as I can tell, there's been "mass immigration" since before there was an "America". Colonial settlers in the 17th century, along with Africans taken against their will. Assorted European immigrants in the 18th, along with Asian laborers and Mexicans taken against their will. So on and so forth. There have always been "immigrants". The US and all the other countries in the Americas are immigrant nations.