Battle of the Celestial Gates

What does the strength of the green army depend on, for example? I made a decent foray with Freya, captured almost all the dwellings on the right side, but at the end of the first month, a demon arrives with 15 arch-demons, almost 30 cave goblins, 50 horses, 100+ skeletons, etc. In terms of development and stats, my Freya can still compete with him, but in terms of sheer numbers, there's simply no chance. No reinforcements came to my aid; they were wiped out by some garrison on the second week, but at that stage, it's unlikely to be possible to defeat garrisons, considering the activity of the yellow faction...