Empires use Death Magic, and Kingdom use life magic. Supposedly this makes the Eastern Empire lands to be Blackened with Ash and roaming with Vile, twisted things, as well as Cool and Powingerful creatures.

The Kindom's land looks more harmonius, and is a true restoration of the land to its Original State. It could potentially be said that while there is a birth-rate in the Kingdom, there is a Death-rate in the Empire. Emperors would be more concerned with how quickly people are dying, while Kindom would be more concerned with how rapidly new people are being born. Im sure there are other elements as well. Also, Life magic could probably suck the life out of Nearby creatures and plants ... potentially Killing them, using that "life energy" to channel magic. Meanwhile, the Emperors do not get to channel such Life energy, but have to wait until the creature actually dies. This, in other words, is death magic. Send a cheap fireball into your own ill-protected cannon fodder in order to build enough mana to command a powerful spell to break the Kingdom's defenses. Meanwhile the Kingdom could suck the life directly out of some peasants in order to strengthen their own defenses. Interesting concepts ... always good uses for some mooks to kill for energies. Now, technicaly the life channelers might devise ways to Suck *almost* enough energy from the soldiers so that they are on the brink of death (1 health point??) however are not actually dead. This could prove some problems, however, since most (or many) soldiers indeed have ONLY 1 health point. With a majority of the others having 2-5 health points (at least at really low training levels). While it would automatically kill units with one health point, they could drain life to create energy without killing as well, if for no other reason than to kill their units would only fuel the Death Channeler's magics as well, so the Life channeler has a special investment in keeping his energy-pets alive. Of course, it would take a very simple one-hit area spell to kill off soldiers drained in such a way.

This was the reasoning behind my answer.. something about being in the east..

Lands in east and west start as barren deadlands.

  Interesting; not sure if I like that

Yeah - consider that your sovereign is tapping the power of an entire 'empire's worth of life/death - including non human life.. plants, animals, trees, insects, fish and especially people are constantly being born and dying at any point. Death and decay is a pretty important part of ecosystems. Presumably, the way this works, is one just gets an allowance of 'death mana' per turn, and that mana is used on more traditional spells, which, in fact, may include traditional 'dark magic' as well as other kinds. Presumably all the magic is somewhat 'flavored' by the mana in which it is made, so it'll probably have 'dark magic' leanings. One might also get bonus mana when something is actually killed, but I have no idea about that.