[jeffersondem]

“The Confederates had been represented (and over-represented in Congress . . .”

The southern states were well represented but not over-represented. Each southern state had two Senators per the Constitution and Representatives as proscibed. At the insistence of the northern states, some people in the south were only counted as 3/5ths of a person.

[LexBaird]

At the insistence of the northern states, some people in the south were only counted as 3/5ths of a person.

And at the insistence of the southern ones, those same people got 0/5ths of the vote or representation in Congress.

[DoodleDawg]

At the insistence of the northern states, some people in the south were only counted as 3/5ths of a person.

In the South those individuals were considered property and not people. They had no rights and therefore no need for congressional representation. As a result the white population was over-represented in the House.