What does Dragon's Army do and should I level it?

Dragon's Army increases the troop capacity per dragon — how many troops each dragon can take into a fight. The tiers give:

• I: +250 · II: +500 · III: +1,000 · IV: +250 capacity.

Why it's huge: a dragon that drops to 0 troops retreats. More capacity = your army survives more rounds before retreating and deals more (damage depends on troop volume). The attrition math (−300 to −600 troops per round) makes every thousand of capacity precious.

➡️ High priority, especially tiers II and III (+500 and +1,000). It's one of the best "survival plus damage" levers in the whole tree.