Answer:
Before slavery became an issue, it is socially acceptable for American people to see that people from a certain race or ethnicity are inferior over the other.
They use that as a justification for all horrible things that they did to these minorities. For example, They enslaved the Black people, heavily overwork Mexican and Asian people on their labor, massacre the native american people to steal their land, etc.
As industrial revolution came into united states, more American people realized that they would no longer need slavery as their labors. They can use machinery to increase their production instead.
This led to a new wave of progressive movement that advocated for the Abolishment of slavery. It opened up people's eyes that they've been using fellow human being as a tool for production and they aware they need to took drastic measure to give them freedom. This eventually led to the civil war which won by the union and force the southern states to gave up slavery.
But the movement didn't stop there. People believe that US faced other social issues that needed to be addressed. So the progressive movement continue to brought attention to problems such as giving women's right to vote, providing legal citizenship for the ex-slaves, Providing workers with minimum wage, etc.
