[Non-Sequitur]

They did not rebel. They parted company. The south did not know when or if slavery would end. If they really wanted to keep slavery indefinitely they could have just stayed in the Union and helped pass the Corwin Amendment.

The Corwin amendment specifically did not address the one issue that the southern leadership was most interested in, the expansion of slavery into the territories. They knew that unless they could take their slaves with them into the territories then the states that resulted could not be slave states. So instead they rebelled and adopted a constitution that protected slavery expansion and slave imports in a way the Corwin amendment could never do.

[smug]

...they rebelled and adopted a constitution that protected slavery expansion and slave imports in a way the Corwin amendment could never do.

True, but it would have been without great risk.