Why do you think immigration to the US decreased during Panics and Depressions?

Shown below.

Explanation:

The US is known to the economic world power though that's shifting. But in the face of economics depression the number of immigrants is likely to reduce because economic opportunity is a major stimulant for immigration, however panic could refer to threat to peace like terrorist attack like the 9/11 event would undoubtedly reduce the number of immigrants.

c. reserves power to the states and people