How did the confederate states rejoin the union?

Answer 1

After the conclusion of the Civil War, former Confederate states rejoined the Union through a gradual political process established in tandem by the U.S. President and Congress. Fundamentally, each state was required to submit to military-led (though temporary) governing by Northern administration as part of the Reconstruction effort. Additionally, each state was required to ratify through democratic process the three "reconstruction" amendments to the Constitution, the 13th, 14th, and 15th.

Answer 2

March - July 1897, under what are known as the First, Second, and Third Reconstruction Acts, Martial Law was imposed on the former Confederate States until they petition for re-admission: To be readmitted the States in rebellion were required to

1). Hold Constitutional Conventions including black delegates

2). Write new State Constitutions acceptable to the Congress

3). Ratify the 14th Amendment, the 13th was not at issue as it was ratified December 18, 1865

It is interesting to note, the above Acts as well as a Civil Rights Bill in 1866 were all passed by the Congress over the veto of President Andrew Johnson.