@roam - i started to use save game lately to avoid these breaks from a campaign

:edit - well the sentence alone makes no sence in your case- i meant when sieging
a settlement to the end to fight it out (in most cases) i sometimes crash at the popup
where you have to choose one of the 3 doors (exterminate etc.) - right after clicking
an option -> CTD -
Now for exactly those i started to save very often.
@Pharao - well if you can't use force diplomacy , at least you could try to convince
them with money. Now if you add_money how much you need to convince them,
you would not be angry at yourself for cheating because you know that you did
it for the purpose of forcing diplomacy.
~S~ CD