Why was Radical Reconstruction "radical?"
First, it should be noted that "Radical" Reconstruction can refer to the Wade-Davis Bill, introduced in 1864, or the Congressional plan for Reconstruction beginning in 1866. In any case, these plans were considered "radical" (including by their authors) because they in various ways sought to bring about first the full and total compliance of the seceded states through the use of coercive federal power. Second, they planned to bring about civil and political equality for freedmen. This in itself was a very radical proposition even for some politicians who had been abolitionists before the war. In addition, the Radicals dramatically expanded the power of the federal government through institutions like the Freedmens Bureau, unprecedented for its time, and more importantly through the use of federal troops to enforce Reconstruction. Another, simpler reason that Radical Reconstruction received the moniker of "radical" is that many of the Republican politicians who supported it had referred to themselves as "radical" before the war, when they sought to curb the influence of the Slave Power. During and after the war, the moniker stuck, and so their plan for Reconstruction was known as "radical."