Why didn't you check your timeline? The proposed 13th Amendment passed out of the House in February 28 and the Senate on March 2nd, both before Lincoln was inaugurated. If by 'confederation' you mean the confederacy, Davis had been inaugurated February 18 and the confederacy was operating under a provisional constitution which protected slavery and slave imports so the Amendment was passed AFTER the confederacy was established. So having protected slavery on their own why would the southern states suddenly call off their secession?
Aha! So they were on their own?
But, but, but, I thought you were saying Lincoln was just invading his own country and asking countrymen to attack one another, not that he was invading separate sovereignties! Which was it?