In the post-Civil War era, immigrants from and were likely to receive the greatest discrimination.

China and Ireland

Explanation:

Due to the Irish Potato Famine many came to the U.S looking for new lives, and were discriminated against and insulted for their looks. The Chinese had it even worse, many protests were held in California and many were racist to them because of the way they looked. Congress eventually passed a law, outlawing Chinese immigration for nearly a century.