Assumption: There is no ACW, but the conflict between slave states and free states remains strong.
Possible PoD: Lincoln isn't nominated, either for havong died before or because he is unavailable. The Republican candidate manages to lose in 1860, and his successor in 1864, while the main battle is fought inside the Democratic party.
With an eye on the Senate and possible amendments, the slave states will probably strive to have as few new states in the territories as possible.
How few are practically possible?
Can Washington Terr. become one state without splitting OTL Idaho off?
Can there be a Mega-Nebraska? Or will there be at least a Mega-Dakota (ND, SD, MT, northern WY)? Might the creation of Nevada be avoided by keeping it with Utah or giving it to California?
Will the southern states try to block the purchase of Alaska, if Russia even offers it at all?
OTOH, without the ACW, might the proposed creation of a slave state in
South California below the Missouri Compromise line of 36°30′ North succeed?