Allow any state, with fiscal means, to withdraw from the union after payment of their portion of the national debt.

Given that the state itself has the fiscal means to be self-sustaining, allow them the right to withdraw from the union after payment of their debt to the federal government; if the state has the means to be self-sustaining but cannot if they pay the entire portion upfront, allow a payment plan to help them withdraw successfully. After doing so institute mutually beneficial trade relations that help both economies prosper and keep close diplomatic relations with the newly founded the country(s) also allow them a chance to sign treaties with the US to deter the possibility of a civil war. given that things go smoothly the separation from the union would be a economic and political step forward, maybe not in the direction envisioned, but it is a step in the right direction.