You could not create a better example of every single thing wrong with what qualified as “demobilization” during the medieval era if you were trying.

Soldiers becoming marauders was always a thing, but the sheer scale of it during the Hundred Years’ War created an enormous shitshow for everyone involved. During lulls in the fighting, these “free companies” would band together and start marauding across the French countryside. These weren’t disorganized bands of misfits with rusty axes and worn-out gambeson – they were professional soldiers who could and would put castles to siege, and could (and did) beat a royal army in a pitched battle.

Their forces were constituted of men from many different territories controlled by or allied with the belligerents, as well as mercenaries hired by the belligerents. Were you French? Good chance your pay was going to be delayed or never materialize for any of the numerous reasons medieval soldiers often got screwed out of pay, and there was also a good chance your farm or whatever was destroyed in the fighting, so might as well get to pillaging. Were you English? Well, you didn’t cross the sea just to be told there was now a truce and you weren’t going to get the pay and plunder you were hoping for, so might as well find your pay yourself. And who were the locals going to complain to, England? (Yeah, they would, since you were doing this during a truce, but that’s the Crown’s problem, not yours.) It was common for these companies to end up becoming mixed groups made up of forces from all sides, which sounds wholesome except for the part where such groups didn’t even pretend to maintain nominal loyalty to any cause but plunder.

The French hated them because, well, they were pillaging France. The English hated them because, given that many of the free companies stemmed from English forces, their actions did a lot to delegitimize the war, making it come off as state-sanctioned banditry rather than a lawful effort to secure a rightful claim, and they made a mockery of armistices (and, in fact, such armistices were what most often spurred their formation and marauding). Also, many territories in what we’d consider France were controlled by England during the war, and those places were just as vulnerable to marauders. They’d frequently rove about to neighboring regions as well, pillaging them too.

Free companies would also frequently raid monasteries and abbeys, or extort them for money, in ways that would make the Vikings proud. At one point, they managed to earn a *mass excommunication* from Pope Urban V when they threatened Avignon. In the end, the Pope ended up having to pay these nominally Christian soldiers to not pillage the place (which his predecessor had also had to do).

The most consistent solution to them was paying them to be someone else’s problem. They were a major impetus for Europe developing standing armies – it turned out to be cheaper to keep soldiers on the payroll than to stop paying them when they weren’t fighting and hope they wouldn’t be soldiers.