This land-grabbing idiocy, called Settler Diarrhea, first of all is a cheat as the AI could never honestly build all those settlers and foot soldiers it pewks out, plus they often teleport themselves to open tiles they shouldn't even know exist, that as they arrogantly wander through my territory.
Invariably, AI towns are built in stupid places all over. I wait until I have a good civ, and maybe swordsmen or knights, and then attack them. They are impossible to defend well being so isolated, plus they produce little for their AI civ owing to crazy corruption. So Settler Diarrhea in the long run works against the AI, but it is dumb and annoying.