First, I agree with Invisible Officer the line refers to “battalions”.
Without getting into the history of the “brigade” formation… Black Powder relies on the “brigade” as its primary “higher” level commander… in effect, your role in the game is to act primarily as one or more brigade commanders issuing orders. Individual cavalry regiments or infantry battalions are simply tactical units with no inherent independent command ability other than their ability to react to charges.
So once you cut through all the wording… the rule is saying a brigade consists of 1 or more regiments comprised of one or more battalions.
So for gaming purposes a “brigade” must have one or more battalions. In most games an infantry brigade will be comprised of two regiments of 2-3 battalions each… any less makes them very fragile. Much bigger than 6 tactical units can cause your army to stagnate on a bad command roll.
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