Question about a feature in Dom 1

[Humer]

As there seems to be a lot of feature-requesting going around, I decided to de-lurk and, well, make A Contribution.

So, in Dom I there is this 'nasty' feature of converging armies and enemy attacking, which I really hope someone clarifies for me.

OK, setup (difficult-ish): I have armies A1 and A2 in provinces P1 and P2. They are both given 'move'-order to province E. Meanwhile, the heretic (henceforth: the Enemy) has her army B1 in province E and issues a 'move'-order to province A1.

Outcome of this scenario usually results in A1 NOT attacking leaving A2 to handle the B1.

My questions: Why? What's the deal with this? And most importantly, how is this handled in Dom II?

I couldn't find this in the "old forums" (comp.sys.ibm.pc.games.strategic), so...

- Humer