[Bull Snipe]

The Constitution of the United States, to wit, Article III
Section 3. Treason against the United States, shall consist only in levying war against them, or in adhering to their enemies, giving them aid and comfort.
Using the strict interpretation of that section of the Constitution, I suspect that firing on a United States Army Fort by South Carolinians, or leading an army from Northern Virginia to invade Pennsylvania, could be considered treason in some circles.

[Uncle Sham]

Once the South left the Union and established it's OWN country there was ZERO possibility of treason against the United States, only the possibility of DEFENDING itself against a northern aggressor. The South had no plans to invade the north or FORCE the north into a union that it did not want. Slavery was LEGAL when the war started and in fact the entire issue of the north fighting the war to "end" slavery in the United States was actually made unnecessary when the South left the union. THEY, by leaving, ended slavery in the United States. The north had offered to enshrine slavery forever before the South left by offering the Corbin Amendment. The north had imposed it's opinion of blacks in the South by having them count as 3/5's of a person for representational purposes.

What gave the north ownership of the South such that they could FORCE them to remain in a union where they were being financially raped by northern interest? The South left, peacefully. That wasn't good enough for the northern financiers who were profiting from the slanted trade and tariff rules resulting in one fourth of the population paying 90 percent of the funding for the federal government. Your monster government today is who won the war. Be proud.