The treatment of immigrants
Immigrants rushed in. Irish, German, Polish, and Italian immigrants weren't always welcomed in the land of the free. The Know-Nothing Party campaigned against Catholic immigration in the 1850s. Signs for jobs often said, "No Irish Need Apply." When Irish workers hungry for jobs replaced striking women textile employees in New England, prejudice against the new immigrants soared. Irish, Italian, and Polish immigrants often spent generations living in ethnically isolated communities. In the years before the Civil War, multi-ethnic neighborhoods and towns were relatively rare.
Most immigrants avoided the South so they wouldn't have to compete with slave labor on the one hand and rich landowners on the other. That situation left the South short of new blood and of any kind of cheap labor except slaves.
Question: How did textile mill owners inflame prejudice against the Irish?
Answer: New England textile mills replaced striking local workers with Irish immigrants.
Problems faced by free blacks
About 250,000 free blacks lived in the South and another 250,000 in the North. Blacks gained freedom through Northern emancipation laws and the occasional goodwill of Southern owners; their children were then free as well. They were in a precarious position. Free blacks couldn't testify in court. If they were assaulted by whites, unless other whites showed up to defend them (which was rare), the blacks never got justice. In the South, they were in constant danger of being kidnapped into slavery. In the North, mobs of poor Irish and other immigrants who resented the competition from free blacks for low-wage jobs often beat them up. Blacks couldn't go to most white schools, stores, or churches. Frederick Douglass, the distinguished black abolitionist, was beaten by Northern rowdies more than once.
Question: How did some blacks become free before the Civil War?
Answer: The number of free blacks in the United States grew because Northern states ended slavery, some Southern slaveholders freed their slaves after the Revolution or in their wills, and freed blacks had children who were then themselves free.