I think it would be a good idea to add an option that would allow the player (and the AI) to break a treaty they have made, but to get a permanent diplo penalty with everyone for doing so (something like: -1:You broke a treaty and for the specific civ in question an extra -1:You broke a treaty with us).

For example:
Civ A has a defensive pact with Civ B. Civ C then declares war on Civ B. Civ A gets a pop-up asking whether it will join the war against Civ C, and if they say no, they get a -1 diplo modifier with everyone, plus an extra -1 modifier with Civ B.

i dont like diplo penalties for breaking treaties!

I had the same idea. In the U.N. I think you should be allowed to break a resolution. Many times, I wanted to build nukes, but I wasnt able after the non-proliferation treaty passed. Yeah, not very realistic. So if you refuse, you get a penalty for the civs who voted yes. At least in BtS you can defy the resolution. If you played Rhyes and Fall of Civilization (great mod by the way), they have something very similar. If you refuse to give away one of your cities in a global election, theres a chance that they will declare war on you.

You can break the 10 turn peace treaties after 5-6 turns. And the -1 bonus against everyone for breaking a pact should only work to a -1 bonus for the other pact signer, and a +1 with the enemy.

Which leads me to my next point: DPs shouldn't be canceled if Nation A goes to war. The other signer, Nation B, should be drawn into the conflict if Nation 2 declares war on Nation A to help the first victim, Nation 1. So..
Nation A and B have a DP. Nation A declares on Nation 1. Nation 2 helps 1 and declares on A, drawing B into the war on A's side becuz of the DP.