A prolonged one in Civ 3
I'm very much an economic player. I tend to turn all my attention to money and tech in the hope of fielding a smaller but very advanced military rather than a massive zerg-rush military. There was me and the Aztecs taking up about 3/4 of the map, with a handful of tiny coastal countries, physically separated from the Aztecs by me, on my Eastern border.
I'd been trading and keeping these countries happy in my hippy economic strategy, when the Aztecs rushed a buttload of Crusaders into my territory. With my cities being minimally fortified and only a token standing army to bring to bear.
Looking like I was in the shit, I formed a coalition of the willing with my tiny friends, and pushed the Aztecs back into their territory until we'd driven a wedge into their country, splitting it in two. I then gifted all the captured cities to my little friends to keep the former Aztec territory fragmented and neutered whilst keeping my buddies happy.