This might actually tie into the suggestion I made in another thread that you could combine setting bounties and forming parties into a single mechanic, by declaring Quests on which interested heroes could embark. It would let you screen applicants, negotiate individual payoffs, and provide a well-defined reason for heroes to work together. (As opposed to the problems you'd see with party-formation in Maj2, where heroes form cliques solely at the player's behest and then amble off on shopping expeditions until you tell them otherwise.)Imagine war as: You set target (as war targets, something like in Victoria 2, war aims), you chose general and give him sum of money. He would than hire number of henchmens, siege engines, better weapons from heroes-blacksmiths, and heroes too. The army than could go on campaing.
So, yeah- one can easily imagine a 'War' flag where you have the option to attach a regiment of footsoldiers or a pair of dwarven field ballistas, and the heroes serves as lieutenants. Or maybe the Barracks building could be an add-on for the Warrior's Guild, and the Call to Arms function would serve a similar function.