That changed in the wake of the South's surrender at Appomattox: The Civil War Amendments explicitly gave the federal government expanded powers. Sure, the southern states were forced to ratify those amendments before Congress would recognize their representatives and senators. But they brought it on themselves; it was one of history's most-horrendous examples of FAFO. And the South was saved from far worse by Lincoln's and Grant's desire to be conciliatory and Andrew Johnson's malign views. (I read a tweet some years ago that Gen. Sherman should have mowed the South like a lawn, with multiple passes.)