The correct answer to this open question is the following.
You did not mention the kind of event you are referring to, neither the time in US history. You also did not attach the options of the question.
However, doing some research, it seems that you are referring to the strict legislation the United Stated federal government had to make after the wave of immigration to America.
So one way the US government responded to this combination of events was to pass immigration restrictions.
The US federal passed the Johnson-Reed Act, commonly known as the Immigration Act of 1924. This legislation established a quota based on nationality origins to provide visas and allow the entrance of foreign people to the country.