Which change was needed for african american men throughout the united states to be able to vote in congressional elections?

It would be the "Fifteenth Amendment" to the Constitution that was  needed for African American men throughout the United States to be able to vote in Congressional elections, since this prevented any government from denying a person to vote based on race. 

When analyzing the american landscape at the time, it can be clear that some women did not support the suffrage movement due to the fact that it would impact their current way of life, leading to fewer protections and safeguarding under the us law, and in their family lives.