In the early 60's people were calling for immigration reform. There was a national origins quota system at the time which lasted until the Hart-Cellar Act of 1965. Then there was a BIG change.
"October 1965, President Lyndon B. Johnson stated that the act “is not a revolutionary bill. It does not affect the lives of millions . . . It will not reshape the structure of our daily lives or add importantly to either our wealth or our power.”
However, apparently it did all it was said it was not expected to do.
"In reality (and with the benefit of hindsight), the bill signed in 1965 marked a dramatic break with past immigration policy, and would have an immediate and lasting impact. In place of the national-origins quota system, the act provided for preferences to be made according to categories, such as relatives of U.S. citizens or permanent residents, those with skills deemed useful to the United States or refugees of violence or unrest. Though it abolished quotas per se, the system did place caps on per-country and total immigration, as well as caps on each category. As in the past, family reunification was a major goal, and the new immigration policy would increasingly allow entire families to uproot themselves from other countries and reestablish their lives in the U.S."
This is history many of us lived through . . . if we were in country. Even so, when we were growing up we were likely not paying a lot of attention to the details - nor doing the research. So it fills in the blanks of what we didn't know at the time about the political environment.