Your analogy is fraudulent and emotionally loaded. Terrorists in afghanistan made an unannounced, unprovoked attack on civilians in another country halfway around the world with massive casualties and destruction. The confederates carried through their long-announced intentions to lay seige to a fort within their own boundaries in direct response to military instigation by Abe Lincoln, who had sent a fleet of warships there to start a war. It resulted in minimal destruction and not a single casualty. The two situations are simply not comparable and as a rule of logic from the law of causality, the invasion of Virginia was not a necessary consequence of the firing on a fort in South Carolina.