Alliances and consequences

[Jxrc]

I noticed that your allies are much more likely to betray and attack you than neutral bordering factions for some reason. In fact, allies will always attack you eventually, against all odds, as if it were forced via script, and usually with their king leading the attack. Is there something I can do to remove this particualr annoyance?.

Unfortunately, the diplomacy is the disappointing part of MTW. Basically, the AI will attack you (irrespective of whether or not it's allied with you) if it thinks that it has a good chance of taking one of your province and if it has nowhere else to expand for a lesser cost (rebel land mainly)

Regarding faction marriages, I always seem to wonder what my princesses are really useful for. If I marry them to another faction, I get an alliance (which may be betrayed) and they get my lands should my king die with no heirs (well, game over unless your are HRE....). I end up marrying them off to some of my generals usually for "good service" as you could call it.

Mazrrying your princess to your own generals is pretty much the best you can do (increases loyalty by two shields). Better off seeking alliances with your emmissaries or bishop, they are there for the long term (at least until they get assassinated) while you princess disappear once they get +/-32.

Princesses of other factions are obviously welcome to marry into my line, since this gives me access to their lands eventually.

Do not rely too much on that one, it happens once every three hundred campaign (happened to me once and I got the game in 2002). The best bit about marrying AI princess is that it enable your princes to produce heirs immediately.

but some factions seem keen to marry every single one of their princesses off to my heirs without prompting, while others outright refuse to marry at all.

Usually only the factions to which you are not allied already will accept to marry their princess to your princes. It seems to me that it is due to the fact that the AI regards a such proposal a bit like an alliance offer (indeed when the AI offer to marry one of your princes it always implies an alliance). Interestingly, that rule is not 100% correct since even when your are allied with all the princess-producing faction, there is almost always one faction that, even though it's allied to you, will constantly accept your offers. Once you get too big for the AI liking, all your marriage proposal will be turned down.