Why did the freedmen petition the United States congress instead of working through their state government?

The petition to the government is provided to the people in the Amendment 1.

Explanation:

In the Amendment 1, the people of the United States of America are given the right to make petition to the government for redress of a grievance or to take a problem to the government to get it solved.

This amendment also gives the rights to the people of the United States to follow any religion of their own choice or to speak anything for putting their views forward and expressing their opinions. They can also assemble peacefully for any reason they want.