Answer:
He thought it was mistreatment
Step-by-step explanation:
As known, in Frederick's time, African-Americans were slaves for a white man. Fredrick Douglass was lucky he escaped from being a slave. And he decided to let his voice speak out for all African-Americans to let them be free. It was quite unusual for a black man to speak out. Only a white man could speak out. And since the U.S government didn't think about freeing slaves before Abraham Lincoln was President, he thought that it was wrong to have a black man be treated like this.