Title? From 1845-1855 one million immigrated to the United States.
They immigrated partially to escape economic hardship.
They also immigrated partially to escape political unrest that included riots, rebellions, and a revolution in 1848.
America was one of the few countries in the world that would accept their immigration.

A good title for the above list would be —

German Immigrants

Irish Immigrants

African Immigrants

Chinese Immigrants