And now on to the incredibly stupid thing I did. Several turns ago, it will be recalled, I took the precaution of sending the garrison unit in Montgomery, which wasn't in danger of attack from the Union's forces, to Selma, which might have been in danger. Over the past two turns I've been so intent on smashing these units in Tuscumbia that I didn't notice that Montgomery is just two turns away, and thus easily reached if my forces could be evaded. And that's what happened -- while the Union army was destroyed, the corps avoided battle and reached Mongtomery. And since sieges occur first during the movement phase, nothing can prevent that corps from laying siege to the undefended city and taking it. This will at the very least cause all production in the city to stop until it's been retaken, and and worst could lead to plunder of the city. (The province itself cannot be taken, since one cannot capture a province that's not neighboring another province one controls. Still, the Union can squat there.)
This corps got down there with its supplies exhausted and must have suffered severe march attrition, but enough survived to cause some trouble.