There are ways to avoid wars. I frequently have games with zero wars. The diplomacy system is very transparent. It's easy to see danger coming and then avoid it by bribing civs and such. Usually, the AI does not break a DoF unless you're supremely weak or they were already plotting against you. If it's former, then there's nothing to complain about. If it's the latter, then I think that's great game design. I like the fact that the AI will disguise their intent by forging a DoF. Of course, it's really easy to see through it, but that's not an issue with the mechanic itself.
Not sure if this is a change with the patch, but it now seems more difficult to see through, in a good way. In the past, a refusal to renew a long-lasting DoF, or a refusal to renew after a maximum of two past DoFs, always equalled imminent war. Now I can have game-long DoFs only to be backstabbed or face a sudden refusal to cooperate (I can still predict, usually, who the civs will be).
The AI now also seems to be more inclined to take account of defensive pacts (even if they're supposed to be secret) - get a defensive pact with a large neighbour close enough to threaten your rival and they may back down. Or, if not, allow you to get peace on relatively favourable terms soon. I usually do this when I see military buildups nearby - make sure to scout a few tiles outside your borders, since an AI will start setting up for an attack quite a while before actually declaring war, so I grab my closest ally and make a defensive pact. Sometimes making friends with the offending civ's friends or denouncing their enemies will make them rethink their attack as well, by improving relations with you.
Don't waste gold on bribery unless you're desperate - better to spend it on units, as the other civ may take the money and not do much. If you have a defensive pact, the civ thinks it's been attacked when you are, so it will treat the attacker as a personal enemy. You can also use pacts to manipulate an attacker into backstabbing its friends (just form a defensive pact with one of its friends, so if it attacks you it will get the large, almost permanent dipo penalty from backstabbing) - damaging the rival's reputation is a much surer way to get meaningful intervention against them, and may build an alliance of sorts that will help you in the longer term - some civs place a lot of value on the "fought against a common enemy" modifier.
If at all possible, reserve bribery just for cases where you don't expect or plan to be involved in a war yourself, but need to keep rivals occupied. In my current game Siam and the Aztecs are currently in a stalemate, although at some point the Aztecs captured the Siamese second city. If it looks as though Monty may win the war, I'll probably bribe (friendly) Ethiopia (who just founded Lalibela on the same continent) to join the fight - I don't want my rivals to become dominant.
Civ V is a very much more political game than the earlier Civ games, which used diplomacy mainly as an aid to trade, and only became political in the era of the UN. It offers a lot of tools under the general heading "divide and conquer" - make use of them.
. I haven't really played after the patch, so I don't know how much the AI has changed. But most of diplomacy is just experience. After so many games of getting double and triple DoWed, I learned how to read the signs and avoid war all together.
