Simple Mass Combat (5e)
This mass combat system provides a simple but mechanically rigorous way to resolve large-scale battles in 5th edition. With this system¸ there's no need to break up armies into discrete squadrons or "units" which then make individual attack rolls against one another¸ thus creating a pseudo-wargame which 5th edition is ill-equipped to handle. Instead¸ the two armies are treated as a whole and their clash is resolved in a few meaningful die rolls. This allows you to keep the focus where it belongs: on the PCs and their actions. The rules are just 4 pages long! The rest of the document consists of helpful appendices and a list of 40 possible wartime encounters. The PCs can participate in the battle as officers or combatants¸ in which case the battle can be resolved quickly and present a fun minigame for your players¸ or the action can "zoom in" on the PCs as they undertake special missions amid the chaos of war¸ thus turning the battle into a climactic event.