sometimes civs just don't go to war with other civs because they're too puny. Most of the time, you literally have to give them a ton of money to get them to go into an alliance. Sometimes they just plain won't. Them's the breaks.
What difficulty level are you on, and what do you have AI aggresiveness set to? On lower levels, with AI aggressiveness turned way down, they are much less likely to have conflicts with each other. Also, don't offer gpt for alliances because the AI will seldom take gpt from you if your rep is the tiniest bit damaged. Just offer up techs, or lump sums. Sometimes RoP or a MPP will do it, although those are very salty affairs to be involved in anyways and most people here would advise against them. Post a save of a game, and one of us forum goons will take a crack at opening up a world war for ya