Rather than Casus Beli I think what this games needs is war justification options. You should be able to recklessly declare war whenever you want.
Instead of simply asking a civ to go to war, you can state a justification for war and put out the diplomatic feelers to ALL civs for their opinions on it. (everyone with an embassy gives you a response) Then, when you declare war you know where you stand and some civs may jump in with you ( or in defense of the target civ ). Also, you can do away with the wait 10 turns dialogue, or being forced to DoW on the spot because the justification and diplomacy has been established and within a timeframe anyone who DoWs the reasons are understood.
"Quebec must be liberated from the Americans!" and they respond "You warmonger!" or "I agree, but I do not have the means to help you" etc...
"Japan must be crushed, they worship heathens!" ( religious war )
"England is becoming too powerful, someone must knock them down to size!"
"Mongolia is hording the worlds crab supply!"
etc...
Your spies can get wind if another civ is plotting against you ( similar to intrigue, but with more data)
Civs can have flavor about what makes them go to war ( some will jump at the chance at religious wars but never go to war for resources or vice versa )