Which group thought that Southern states should only need to accept abolition before being readmitted to the Union?

The radical republicans

Explanation:

From the outset of the rebellion in 1861, Lincoln's overriding goal had been to bring the Southern states quickly back into the fold in order to restore the Union. In early December 1863, the president began the process of reunification by unveiling a three-part proposal known as the ten percent plan that outlined how the states would return. The ten percent plan gave a general pardon to all Southerners except high-ranking Confederate government and military leaders; required 10 percent of the 1860 voting population in the former rebel states to take a binding oath of future allegiance to the United States and the emancipation of slaves; and declared that once those voters took those oaths, the restored Confederate states would draft new state constitutions.

Lincoln hoped that the leniency of the plan-90 percent of the 1860 voters did not have to swear allegiance to the Union or to emancipation-would bring about a quick and long-anticipated resolution and make emancipation more acceptable everywhere. This approach appealed to some in the moderate wing of the Republican Party, which wanted to put the nation on a speedy course toward reconciliation. However, the proposal instantly drew fire from a larger faction of Republicans in Congress who did not want to deal moderately with the South. These members of Congress, known as Radical Republicans, wanted to remake the South and punish the rebels.