Geoff7:

The American Colonies never joined the British empire of its own volition. The people were never consulted and their loyalty was merely assumed for King and Country.

The American colonies were formed on land acquired by Great Britain, the colonies were created by charters granted by the British government which in every case acknowledged British sovereignity, and the European inhabitants of the colonies immigrated here under the aegis of British colonial governance. So suggesting that we just decided that Britain was no longer relevant and weren't in fact treasonous rebels is wishful thinking. Even our founding father recognized they were engaged in acts that would be considered treasonous once they adopted the Declaration of Independence.

The southern states that left the union contended they had a right to unilaterally withdraw from the union, a right that was uncertain and unrecognized by the Union, but was at least arguable. By contrast, our fathers in Philadelphia appealed to "God" and the "laws of nature" in the Declaration precisely because they had no basis for secession under law, and knew it.

Now I'm not suggesting that the Southern secession movement was the moral equivalent of the American Revolution; quite the contrary, as the primary purpose of the movement, at least from the persepctive of the southern elites, was to preserve the slave economy, including both slave ownership and favorable tariff laws. However, the southern states had a far more arguable legal case for their actions than did the original colonies, which had none whatsoever.