Some wiki digging reveal that mongols' ancestors (Ruanruan) cultivated the land from the VIth century onward. Apparently they cultivated primarily millet, and the traditional nomad class was a subset of the total population, and depended of the farmers for their survival. If you want to start a Götürk (VIth to VIIIth century) band and start raiding for cattle and horses, you need to be backed up by a tribe of laborers.
And what about the Huns, or the Turks? What you seem to be arguing is that the Mongols were originally an agricultural people that then transitioned into a nomadic one, in any case that detail is not relevant both because it still means we have about 1400 years of Mongols as nomadic herders. There also a whole load of other related nomadic peoples whose agricultural origins you have not established.
The irrelevant historical details aside, not much of what you are saying makes any sense. You have no need to raid for cattle and horses, because those things reproduce themselves on their own, meaning that you don't need anyone to back you up in order to steal them, since stealing them is not needed.
DF makes things interesting though with goblins that don't need to eat, fulfilling a fantasy world requirement in ways that could never happen in real life.
It also shows natural consequences that are generally unintended by most fantasy writers. For instance, the elven immortality. You make elves immortal, you will naturally grow their population at lightspeed because they won't stop breeding unless they are killed. And since immortality means an infinity of generational overlap (where threeto four generations can overlap for humans), an elven warlord has access to an unimaginable amount of manpower.
I tried to explain this to warhammer players with some numbers, even without considering the exponential population growth, a population that lives for 1000 years can line up 25 fighters for each fighter of a population that lives for 60, due to generational overlap. High elves do not even need to go to war, they can just outbreed everyone... which is the reason why it's important they remain tribal in DF
Such nonsense. Exponential population growth is not how actual creatures ever behave in real-life, for the simple fact that it will simply result in them all starving to death in the end and going extinct. Thus the potential reproductive rate is not the actual reproductive rate, the former nearly always exceeds the actual rate because to reproduce exponentially is suicidal in the long run. While the longevity of the creatures increases the potential reproductive rate, it does nothing to increase their actual reproductive rate which is constrained by the same factors that constrain all other lifeforms.
If High Elves bred exponentially as you say, then they would soon enough end up exploiting the entire food resources of Ulthuan. At which point either they would either stop multiplying exponentially or they would all starve to death, resulting in no more High Elves. That the potential repoductive rate of High Elves is higher than that of humans, matters very little because the potential reproductive rate of humans (about 20-30 children per woman) is far higher than the actual average reproductive rate of 1-3 children (at the moment). The thing here is that the potential reproductive rate of elves is essentially infinite, the actual reproductive rate is in no way affected as elves like humans do not breed to their full potential reproductive rate.
The effects of immortality instead are basically social and these were not really understood by most fantasy authors. You have a very high adult to child ration to begin with, the number of children in society is tiny compared to the number of adults, meaning the costs of childcare are negligible. Then there is the fact that very distant ancestors coexist with all the generations of their children means we end up with a situation where a person can have thousands of children+grandchildren. This messes with the family structure, which in turn will effect the whole societal development in ways that are pretty much never considered.