Army Strength is a number used in calculations for Diplomacy, as well as how many stacks neutral armies will be split into.
For neutral armies, Army Strength is the sum of the AI Values of the creatures in the neutral army.
For players' armies, Army Strength is the sum of the AI Values of the creatures in their army multiplied by the commanding Hero's sqrt((Attack × 0.05 + 1) × (Defense × 0.05 + 1))