I think it's population and transportation but I'm not sure
After the Civil War, 4 million former slaves were looking for social equality and economic opportunity. It wasn't clear initially whether they would enjoy full-fledged citizenship or would be subjugated by the white population.
In the 1860s, it was the Republican Party in Washington — the home of former abolitionists — that sought to grant legal rights and social equality to African-Americans in the South. The Republicans — then dubbed radical Republicans — managed to enact a series of constitutional amendments and reconstruction acts granting legal equality to former slaves — and giving them access to federal courts if their rights were violated.
The 13th Amendment, which was ratified in 1865, abolished slavery. Three years later, the 14th Amendment provided blacks with citizenship and equal protection under the law. And in 1870, the 15th Amendment gave black American males the right to vote.
Five years later, Congress passed the Civil Rights Act of 1875, a groundbreaking federal law proposed by Republican Sen. Charles Sumner of Massachusetts, which guaranteed that everyone in the United States was "entitled to the full and equal enjoyment" of public accommodations and facilities regardless of race or skin color.
The answer is b changing the way americans thought of the government i know this cause i had this test before
