What was the last effort to prevent the south from seceding?

The Crittenden Compromise introduced by senator John Crittenden on 12th December 1860 was the last effort to prevent the secession of the South. It was aimed to resolve the secession crises by political negotiations; allowing the existence of slavery in southern slave states and to re-establish the Missouri Compromise Line. The proposal failed to get the required approval because many southern states already began to secede and so did not vote on it.