Brett Devereaux has written about this a bunch at his blog A Collection of Unmitigated Pedantry, here's the best summation I could find on a quick search:

On the other hand cohesion is the force that holds a specific unit together through the power of the bonds holding the individual combatants to each other and/or to their (generally junior or non-commissioned) officers. There are a lot of ways to build that cohesion: people are generally unwilling to abandon neighbors, close friends and relatives, for one. They are also reluctant to expose themselves to shame at home for having done so; shame is one of the few things people fear as much, if not more than, death. For armies that can’t rely on that sort of organic cohesion, it can be built by reconstructing the soldier’s unit as his primary social group. Drill can do this: it creates an experience of shared suffering and achievement which bonds the soldiers together creating strong ‘artificial’ cohesion.

https://acoup.blog/2022/07/01/collections-total-generalship-commanding-pre-modern-armies-part-iiic-morale-and-cohesion/