[DeadlyShoe]

It's just how the game is balanced. Troops and mages are at a fixed gold cost, and after you get 2-3 forts up gold is your limiting resource. Mages arn't as good at troops per-gold in the early stages of the game, but as magical research continues they become more powerful to the point of obseleting troops.

Things that affect this balance are the cost/effectiveness of troops, the cost/effectiveness of mages, and the rate of magical research. Setting magical research to difficult or very difficult makes troops relevant far later in the game. The relative effectiveness of troops vs mages for cost depends on nation and era.

Take for example MA Ulm. A Sapper has a Crossbow that fires an armor-piercing projectile every two rounds. At the start of the game, a Priest Smith can cast Flying Shards... which makes him about equivalent to 2-3 crossbowmen at most. With some research in Evocation, though, that Priest Smith can cast Iron Darts, a volley of several armor-piercing bolts each round for as long as the priest remains able to cast. This uprates him to being competitive with about 10 crossbowmen (roughly). With a bit more research, that Priest Smith can cast Iron Blizzard, a similar spell that throws 30 or more bolts, making him equivalent to 60 crossbowmen in sheer firepower....for as long as he remains conscious, of course.

A larger number of sappers still has some advantages, in terms of morale//endurance//being able to soak enemy fire. But it is that point at which you are considering your troops as chaff and your mages as doing the real work. An army with a couple more mages can beat an army that spent that money on troops instead, as long as you have a certain minimum of troops.

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A good starter blood nation is MA Abyssia, IMO. The 'Soul contract spam' strategy using Demonbreds (it's in the index) really clued me into blood.