Jamie,

"In light of your conclussion that secession was illegal prior to the war how do we account for the United States not punishing anybody for rebellion or treason."

Well, actually people were punished. Andrew Johnson implemented a plan that disfranchised the upper class in the South (who he and many others blamed for starting the war), requiring them to personally seek a pardon from him. The system was quite faulty, though, as Johnson began handing out wholesale pardons within months.

Part of the problem with the "punishment" issue was disagreement within the federal government. Lincoln preferred to let the South in fairly easily, believing that punishment was both difficult and counterproductive to reunification. Radicals in Congress wanted a harder-line, which placed former seceded areas under military control for a short time.

In fact, many people today believe that the South was punished too hard during Reconstruction.

Now, to clarify one thing, I do not believe that secession as a whole was illegal before the war. I believe its legality was undecided and unclear, and that the Deep South pushed too aggressively and arrogantly in trying to establish the matter. Secession was a legal matter. When the federal government challenged it (or denied it), the Deep South chose to defend their action with guns, not with the judicial or legal system.