First, the forces of Union! Using the DBA 1500+ expansion rules and army lists, I've assembled what will be my fundamental Union force:
The massive majority is Rifles (Rf), who are ten of the twelve bases. The remaining two are the Cannon (Cn), and the dragoon cavalry (Dr). I did this primarily because I wanted to have the Union to be pretty infantry-heavy, so the boys in blue wouldn't very often find themselves outnumbered other than locally. I had to have artillery of course, plus some cavalry force, however inadequate, for scouting work. The full list is: 10xRf, 1xCn, 1xDr.
Next up, the Rebs:
Defined mainly by the Union force, I found myself getting basically the same army for the south (the army lists are too flexible and you can form whatever force you like) and then adapting it to get the numbers of infantry down. 7 bases are the ubiquitous Rifles, plus a single Cannon again. I gave the army two cavalry bases so they could have an 'edge' tactically over their rivals (as was historically the case.) The final two were a troop type wholly absent in the Union army, light infantry classed as Jagers (Jg). These would represent lighter concentrations of troops that could support the friendly Rifle bases, and pin down enemy ones. Quite a good way to represent a smaller Rebel force confusing and distracting a more tactically clumsier Union rival, as was so regularly the case - especially in the earlier part of the war. Full list is: 7xRf, 2xJg, 2xDr, 1xCn.
So, let's prepare for some fighting! Here's a close-up of the Central Belt, which you can no doubt view on any internet map site. I've marked up the one below to show the situation.
The rebel forces are mainly around Stirling, with a smaller force in the west around Dumbarton. They're linked by the Forth valley, which runs between them and to the north of the large range of hills in the middle. These hills are the Campsies, and although they block any Union movement, the Rebel forces are too far apart from each other to be mutually supportive. In other words, if one gets attacked, it's on it's own and won't get any help from the other until it's all over!
Not that attack is particularly likely anytime soon. The Union forces are typically scattered, but for a massive concentration is located on the critical city of Glasgow. No real move north to Stirling is possible in strength until this city is 100% safe against a rapid descent by the rebel force at Dumbarton. Consequently, the opening Union moves in the war are decidedly meek. Work begins on fortifying Glasgow, to protect it's garrison. A small component of this force is sent north to Kilsyth, in order to secure North Lanarkshire and prepare the way for a stronger advance later (it keeps those 'On to Glenrothes!' boys in the newspapers happy...)
However, Rebel hopes of success will not be met by sitting passively back, especially when the chance of a bold stroke is there! The chance to establish an inferiority complex and upset the Union in their heartland is too good to pass up! Half of the Rebel force in Stirling is kept in place to prevent it being taken, while the other half strikes at the 2PP town of Falkirk, aiming to wreck the Union force in the area and cut one of the most direct links between Glasgow and Edinburgh. The Union force moving forward at Kilsyth will be of no support, as to come to Falkirk's aid would mean moving away from supporting Glasgow. The meddling politicians in the Capital would never allow it! Looks like we have a straight one-to-one fight coming up, on the banks of the small river Carron, to open the war.