I am curious, what world sizes/difficulties are most of you playing on, who constantly have the AI declaring "pointless war"?
My experience has been... Yes, a lot of wars are just flash-in-the-pan wars which don't amount to much. On the other hand...
I usually play emperor/huge with 13 Civs total. As a result, if the game continues late, the map is simply too large for me to possibly have militarily dealt with more than a few people - too much distance, too many diplomatic anthills I can't afford to kick, and simply too many targets... And whenever you raze a city, someone else is going to build a new one there, so long distance wars result in weakening one opponent and making another one bigger. The AI, being set to noble, always, can afford to have way more cities than you, so, they tend to get pretty damned huge by the end.
In a big map like this with lots of people, religious lines are usually quite stark, and diplomacy is an absoltuely uncontrollable nightmare. Oftentimes what I find is that, somewhere out in the world, one or two "trouble" Civs are beyond my power to do much about them - and they come back to bite me in the ass *hard* at some point.
For example, I was west coast on a huge pangea recently with Louis and was just about to get grenadiers... I was Buddhist, had spent a great deal of the game at war with nearby civs and had a very nicely sized civ with a really quite respectable military. Then it came.
Monty declared war on me and *holy ****.* Must have been close to 60 technologically competitive units came spilling across my border, and waves actually followed behind those blowing past my border cities one by one, pillaging and destroying everything... I actually got wiped right out - by a CPU.
I've seen variants of this happen with Genghis and Kuglai before, also with Alex and Isabella. Never on smaller maps/lower difficulties though - always on huge/emperor or above.
I know for a fact that the AI has the power to put out some frightening, if not spectacularly planned, war efforts... Though, a vast majority of the wars they make are still piecemeal. I honestly would like to see more wars like Monty waged on me that game, but, I promise you, if you guys are on the right difficulty/right map type, you will see some pretty scary CPU attack forces coming your way. Not perfect, I know, since you should see things like this on all difficulties/map sizes... But it least it can happen.
PS - play a religious game sometime and convert a few people to whatever religion you founded so you can see into their cities. Some civs (Julius Ceaser, Monty, the Khans, and a few others) have absolutely ridiculous unit buildups which a player can't dream of affording without some very high-yield shrines... That is, if you give them time to do so. I think a good part of the reason why people never see the CPU wage big wars is because they never give it time to build up units - many people seem to play small maps and extremely aggressive games, wiping out most of the competition long before it has a chance to do much. If you play on large enough maps with enough CPU's on a high enough difficulty though, you absolutely cannot help letting some of them build up, and this results in the **** really hitting the fan sooner or later.
Edit: Oh, one more note... One thing I suspect, but can't confirm, is that the slower the game speed, the more time the AI has to stew and get pissed off at you. I prefer going epic speed, and though units are coming in more slowly, it gives that many more turns for the opponent to decide to declare war on me, for my blatent Buddhism (or whatever) to piss them off and push them towards hostility. I think this is a contributing factor for long distance wars - sometimes, on faster speeds, the game is just over too soon for hostilities to really set in. Not the case on slower speeds - or at least, so I've gathered.
. in that case you would have had the seas flooded with ships! 
