The United States does not have a restrictive immigration policy. Donald Trump wants it to have a more restrictive immigration policy. The US has the largest foreign born population in the world. Source.
Many of the countries with a higher foreign-born percentage are considerably smaller. Only the United Arab Emirates, Saudi Arabia, Australia, and Germany have more than five million foreign born citizens among countries with a higher percentage than the US. Many of the larger populations are in Europe, where they may reflect migration inside the European Union. That kind of migration exists in the US as well, but is not counted as immigration.
The US adds about seven hundred thousand people a year by naturalization. While 2017 was lower than 2016 and 2015, it was higher than 2014, 2011, and 2010.
The US adds roughly a million people a year legally, mostly as temporary residents. Some of these may naturalize later, but some return to their native countries.
The US has about eleven million people illegally in the US.
Immigrants have more children than US natives. Your source includes such children in its count. So the leading "immigration" method is to be born in the US. Most sources would not consider them immigrants, but apparently your source does.
The next leading method is family reunification. This includes spouses as well as relatives (often of the spouses). So if someone naturalizes, that person can then sponsor parents, siblings, children, etc. This is about half of legal immigration.
Some other sources:
- The diversity lottery.
- Military service.
- H1bH-1B and other temporary visas.
- Children can be adopted.
