What's up with the AI?

I just sat through 2:30 hour game against two hard AIs and one AI as my ally.

Usually this is a matter of an hour or 90 minutes, depending on my mood. However, this game was just atrocious, as Hiawatha, my ally, would sit his 200 pop cap army in his base and not fucking move it. I might not be good at the game and I do like a challenge, but fighting with 200 pop against 400 pop isn't fun or really challenging. It's just frustrating.

In other games my AI ally moves on and starts stomping our enemies as soon as 20 minutes into the game. Or activating a trade victory.

Why is the AI so inconsistent in its behaviour? And why is it not attacking at all? Even if it sits at 200 pop?