Quote Originally Posted by Aenlic
There's a little trick to getting your sons married.

You're best chance at succeeding is to find a princess from a faction with which you are not at war and yet with whom you aren't allied. Keep track of which faction's princess you sent your agent off to see. It always seems to be the case that you'll receive a standard offer of alliance right before the proposal goes through for that faction. Turn the alliance offer down and BOOM! you'll have a marriage. If you accept the alliance offer prior to the marriage event, then the marriage will be turned down in most cases. It seems the AI factions would prefer an alliance without having to marry your offspring; but they'll take the marriage offer just to get the alliance if they're forced to do so.
I also find I have most success if the other faction is sending or has just send an emissary to obtain an alliance. Whenever I spot diplomats heading for my faction leader I send an emissary after their princesses. This gives two advantages: 1) I gain a princess and thus (hopefully) early heirs; 2) my emissary gets a valour star and not theirs.