Leave them alone.
Ignore them.
Let them slaughter thousands of their own citizens, nothing to see there. (Telling them its against the various conventions won't work, they ignore everyone.) Afterall, they are only killing their own.
Let them keep funding Hamas, Hezbollah and The Houthis. They only want to wipe out Israel, no big deal.
Let them cause terrorism through the middle east, nothing to see there.
Let them continue to attempt terrorist attacks in the UK, afterall, our counter intelligence have foiled them so far....
Let them continue to develop nuclear weapons until they have them and use then, too late then, but oh well, there you go.
No of these things which have already been done worked either. They don't follow rules, conventions and guidelines. The regime must have full control. But hey ho, no problem. Then one day, it's too late. We should all ignore them and what they do and all will be fine and dandy 😊
Happy days