Which countries did most immigrants to the united states come from in the antebellum era?

Most immigrants to the United States in the antebellum era came from Germany and Ireland.
There were various reasons why they emigrated into the States, but the most important one was civil unrest in their native countries. Also, they couldn't find jobs home, and they heard that America is a land of freedom and opportunity, so obviously they wanted to be successful too. 

The american civil war