Why do civs sometimes declare war on you...

[LoneDragon]

...and 50 turns later you have yet to see a single soldier from them?

 

[Gamewizard]

May have been bribed into war.

 

[Rosty K]

Sometimes (or even most of the time) they just use the joint war as part of a trade deal for something completely different, so naturally they never show up then, cause they never intended to. When they do really mean war, they will get some units to your borders first.

 

[LoneDragon]

AIs are some opportunistic A holes...I was just in a spot where no one could touch me...and instead of declaring war on Arabia when they attacked a city state I was suizerain of, I lined up all my troops in a blockade....
So of course, as soon as Peter snakes my suizerain status and scatters my troops, Arabia surprise attacks me...and then Russia a few turns later....after all the times in most games where I'M the warmonger for initiating a surprise attack...

 

[Orange1861]

Yeah, the AI isn't very good at desicsion making until about King difficulty. I still see this throughout the games, but they are more likely to actually attack in King.

 

[LethalLeigh]

Before the Macedon/Persia patch I was playing the Greatest Earth Map. I had all 22 Civs in the game a couple had been defeated by the time I gained contact with everyone but I was mostly friendly with all Civ's. when out of the blue for no reason 12 of them declared War on me 2 at a time over 6 turns. 2 of them were declared Friends. I assumed they were bribed into War via trade, and well I though I was in for a hell of a fight.
BUT only 3 Civ's sent units against me and I was able to fight them off with little loss. The others did nothing other then ask for peace 15 turns later. Most of them were on the other side of the map and I shared no borders with them at all.
So I think that the AI will do thing like DoW thinking they wont have to fight.

 

[isau]

The main reason is that AIs that enter Joint Pacts don't yet have a mission in mind. They are accepting the bribe and have no real intention of fighting you. As weird as it may sound, its not without real world precedent. Sometimes nations declare wars but don't actually engage in them.

 

[LoneDragon]

For the Joint Pact, don't they both have to declare war at the same time? And, if not, I'm also pretty sure I have had this happen with only one civ declaring war.

 

[king of nowhere]

sometimes it also happens that a civ actually wants to invade you, but it shares no border with you and the civs between them and you don't give them open borders. I've relied on that on ooccasions.