DaoistbmKU1Q
I think that for him to have power in the war, he must strengthen his house, which he cannot do with his father and older brother alive, he doesn't need to know how to read and write, or hold a sword to be lord, just to be the older, so as he is going to the eagle's nest, he may end up dressing up there, and eventually due to the lack of heir becoming the lord, which has to happen early, to have time to again create his strength, already that nobody fights wars alone. due to the butterfly effect, you can remove the older brother, and during the rebellion, the father, making him the lord, since the karstark territory is northeastern north, he can bring the people of the true north to his territory.
You keep saying he is using life energy for his magic. Does that mean he spends his life force/lifespan to cast spells? That is what I am getting from your wording. You never specify if he slowly gets that energy back over time to refill him and not loose something like an equal exchange of life force/lifespan for casting magic.