What does Army Expansion do in the War Tactics tree?

Army Expansion gives +1 army slot per level. You can deploy up to 5 armies at once on the map and in combat — every extra slot is one more army hitting at the same time.

Why it's central: combat calibration shows that a single army can't empty a full defender (it stalemates over 10 rounds without killing it). You need several waves — so you need several army slots.

➡️ Army Expansion is a high priority in War Tactics: more slots = more waves = more tiles and seats taken. Level it early in the Reign.