Not sure if this is funny but I was going for a nice domination victory. One CIV left, think it was Carthage, and I was just taking city by city without much strategy involved.
In terms of power, I had more than enough armies and units (modern armour and mech enf.) to be able to advance each turn taking at least one city while garrisoning the rest against what would usually be about a 10-15 modern armour counter attack.
That continent was huge, and nearly all of it railroaded, and obviously all mine with not one city garrisoned other than the front lines. And because it was all occupied territory, cities were for the most part spaced out CxxxxC and the influence didn't cover all terrain.
Then, on one of my turns I took this city which had a ton of cultural influence, and which opened up a gap in my controlled front line territory.
Next turn, instead of the 10-15 or so modern armour counter attacking on a city, they all bypassed everything and through uncontrolled terriory on railroads managed to get to and take about 10+ cities back from me right behind the front lines.
It was incredible, they were able to sneak through and almost each unit went to a different city taking it over. Nearly their entire initial territory before the war was won back in one turn.