After all, what kind of medieval king doesn't assume the same powers as Oliver Stone's Nixon who reckoned he could 'bomb whoever he liked?' Well, you might not get impeached for stabbing your neighbours in the back but you are going to need a good reason to carve up their territory and take a slice for yourself. If you've never played CK II you might not understand why an unjustified war would be such a big deal. The other alterations will come in battle itself, specifically sieges. That could be a dramatic change, given that one of the most important aspects of CK II is the need for a Casus Belli to not only declare war but to inform the goals of a war. The major shift will be in the causes of war, which will no longer require justification in every instance. We already knew about upcoming geographical expansions in Crusader Kings II, making areas that were previously impassable playable, but fresh news arrived in today's dev diary and it involves changes to fundamental systems.
Forget everything Fallout has ever taught you because war is changing.