how to make peace?

I'd like to make a ceasefire with my enemies, but somehow they never accept it, not if on the brink of destruction, not even when there was no harm done...

I know, there is auto-ceasefire when we lose contact but that is not always feasible. (btw I realized I also have to remove my agents from my enemy's soil, not just the ships...)

Other than that, how can I persuade my fellow christians, muslims and orthodoxies that we should stop fighting for the time being...? Any ways to help it? Or force it? :)

I don't think you can force it, especially if you are both catholic and the Pope keeps calling you off every two years. However, they seem more likely to accept a cease-fire if they are really on the ropes, or are being threatend by another neighbor. So beat them up and then see if they will accept, or wait until someone else is gathering at their borders and try then.

They may be more willing to take a princess than an emissary - if you want send them one.

They may be more willing to ally if they don't have any other alliances, so kill off their agents and murder any foriegn agents that are heading their way.

The other thing that can make a difference is the number stars your agent (emmisary/bishop/princess) is carrying - the more they have the more likely you are to get a cease fire. Take a look through your agents and send the best one.

Just because they accept a cease fire doesn't mean they won't turn around and attack you in a few years. I've been through this repeatedly with Spain and Argonne - they attack, get spanked and loose two provinces, the Pope calls me off, I often get a cease-fire, and within 5-15 years they attack again and we repeat the process.