"A year is okay" but "just before declaring war is not" is poor policy: how long beforehand does it need to be declared in order to be okay? Determining the legality of the move by how long ago it was declared only sets up arbitrary rules that no one can predict or understand.
You seem to be deliberately ignoring the fact that there's a lot more than time involved here.
And no, it would not be easy to code. Because not all secessions are made with the purpose of carving out the enemy realm. Duchies can secede by betrayal during war, or to avoid the fate of the central government, and that has nothing to do with plopping a colony in the heart of enemy land. This is what this secession does, however.
So are you saying that any secession during wartime that doesn't immediately declare war on its parent realm is a strategic secession?
And I already named a ton of advantages seceding grants. At least now the city doesn't risk revolting just because it's so far from the capital and troops cannot make it on time for maintenance work. This alone is a serious blow to Enweil. IVF doesn't need to boast a huge army in order to push Enweil further down.
So you agree that Enweil has more or less lost the war already, too. If you are attempting to argue that if Riombara had kept Iato, Enweil could have won the war, but now they can't, you're not doing a very good job of it.
