From page 97 of the manual for Gary Grigsby’s War Between the States.
Movement Tips: The good news is you don’t have to count movement points, but you may be left wondering why you can’t make a move. Is it the or reaction phase? it winter? Does a leader with attached units have initiative? Are you moving from a friendly region another friendly region or an enemy region? What are leader specialty skill ratings and is one type of attached unit dragging entire force ability down? there a transportation line across river you are trying to cross? Has rail unit you are use for been demolished? The problem of movement becomes even more difficult when you get a combination of the above, such as reaction in winter with a force without leader initiative. It can be frustrating at times, but we think it effectively portrays reality of moving forces during American Civil War.
You know what else would be realistic? Being told why a move is invalid, so the general can do something about it. I doubt McClellan just stared at a torn up railway and wondered why his train wasn’t moving.