What condition allowed Southern states to be readmitted to the Union following the Civil War?

The condition that allowed Southern states to be readmitted to the Union following the Civil War was the requirement that 10% of the voters in a state take an oath of loyalty to the Union. This specific approach was part of President Abraham Lincoln's plan for Reconstruction, known as the Ten Percent Plan. It aimed to facilitate a speedy and lenient reintegration of the Southern states into the Union.

Under this plan, once 10% of the voters in a state swore allegiance to the United States, they could establish a new state government and apply for readmission. This strategy was designed to encourage Southern states to rejoin the Union quickly and with a moderate approach, instead of imposing harsh penalties or conditions that might incite further resentment.

Other options presented focus on different criteria that were not relevant to this particular context. For example, ratifying the Constitution refers to a foundational requirement for the establishment of the state itself rather than a post-war condition. Similarly, electing a new governor or paying war reparations did not constitute a condition for readmission in the Reconstruction era. These alternatives highlight different aspects of governance or recompense but do not align with the specific requirement of loyalty oaths that characterized the post-Civil War readmission process.