In the one "open-forum" MP game I have participated in until now, I repeatedly and violently trashed the armies of those players who made war based on that mistaken belief. It helped that several of the players were also under the mistaken belief that fortresses weren't all that important because they only contain a few thousand men.Tonioz said:- controller of the province receiving same or near same support in the province as owner+controller. Owner, who losts the control, gets same or near same support, as non-owner & non-controller. That made EU3 like CIV - no matter who owned the province, important who controls it. That kills the eu2 idea of biggest advantage of the defender - own lands. So no wonder that modern eu3 warfare (couple of months ago, when i asked several guys who play it), is gathering horde and moving against other horde.
Using smaller and more maneuverable armies and only uniting them for big battles remains as important in EU3 as in EU2. As soon as you get past the early game and start building fortresses big time, the depth of your country and attritional warfare is as important as ever for bleeding a numerically superior enemy to death, and taking the fight to the enemy means you need to have a plan to deal with your own considerable attritional casualties.
Sure, making "one big horde", moving against another horde, and assaulting his provinces one by one and crushing him is eminently possible - if your opponent has no defensive depth or chooses not to utilize it based on him playing by the horde strategy too. If he has defensive depth, knows how to use it, and has built defenses, it is a great way to lose your horde, exhaust your manpower, and be methodically taken apart after your fury is spent.
I don't have the numbers to support this, but it sure feels like highlevel fortresses in EU3 (L4-6) are even harder and more risky to assault without waiting for a breach than highlevel EU2 fortresses were.