You know you've won when...

[Spart]

This may prove to be a bit more of a challange but I think a bit of change is always needed,

You know you've won when a superior army is marching on its way to your capital, you've won because you capital is Moscow and their general's name is NOT Genghis Khan

[macsen rufus]

You know you've won when your top generals look bored, yet spend a lot of time sharpening their knives and offering you glasses of wine that don't smell quite right....

[TruePraetorian]

You finally finish the manhattan project before any other country and test it.

[Ibn-Khaldun]

You finally finish the manhattan project before any other country and test it.

And it all happens in 13th century

[Barbarian]

When strict and stubborn tyrant emperor (your enemy) wants to start negotiations.

[Genaral Julis]

When the enemy orders a vast amount of beer.