I find in my games, that AI Iroquois starts strong, and if your looking at the map continue to fill in all empty spots, but that if you are instead motoring AIs relative science rankings they tend to start collapsing in mid game as the AI doesn't build enough science buildings to keep up with the increased per city science costs. (Standard map size; perhaps on bigger map sizes where the per city penalty is less they don't run into this as much)