Why would congress not seat newly elected senators and representatives from southern states?

Throughout the history of the United States Congress there have been times when members of either chamber have refused to seat new members. Article I, Section 5 of the United States Constitution states that, "Each House shall be the judge of the elections, returns and qualifications of its own members, and a majority of each shall constitute a quorum to do business; but a smaller number may adjourn from day to day, and may be authorized to compel the attendance of absent members, in such manner, and under such penalties as each House may provide." This means that members of the House of Representatives and of the Senate can refuse to recognize the election or appointment of a new representative or senator. They can bar the individual outright or refer the matter to a committee for inquiry. Powell v. McCormack (1969) clarified the issue of the scope of powers of the Congress to refuse to seat an elected member. The Federal Contested Elections Act of 1969 currently lays out the procedures by which each House determines contested elections.