What workplace challenges confronted urban workers and farmers in the late 1800s.

low wages and long work days

The "oppressors" in the quote are the Britishers who ruled over the American colonies.

And the "wise" men are the forefathers of the whites who revolted and fought for their independence.

Explanation:

Frederick Douglass's "What to the Slave is the Fourth of July?" explores the constitutional relevance of slavery even after America got its independence. He argues why blacks were still oppressed even after America has had her fair share of oppression from the British and celebrated with great pomp and festivities once independent.

In his statement "Oppression makes a wise man mad", the oppressors are the Britishers who oppressed the whites under the colonization system. The "wise" men in this line refers to the forefathers of the white men who were wise enough to protest and realized the oppressive state they were subjected to by the British. And it was this madness that led to the fight for independence. This statement is a reference to highlight how the whites were also put under the Britishers, just like the blacks and slaves were under the Americans.