Hmm, I'm just thinking that if Louisiana, Mexico , BNA and Tecumseh nations would like to take care of a future problem, slicing off the Prairies from the rest of Jackson's USA would be rather simple.
True, but the thing is Jackson and the American military can also read a map. So I would wager in addition to the Jackson line in general that corridor is highly fortified with large garrisons on hand to prevent such a cleaving. With how close to losing the Northern Prairie they were in the peace conference I am guessing defending their last frontier is at the forefont of their military projects.
So it might be doable but such a coalition fpoce would pay a very steep price for it and then face a possible pincer.