why does every savages are always Mongolian?????

or dark skinned, it’s so blatantly racist and colorist

I think in this case is because they are nomads that move on horseback and the think populations you think about are the ones in the steppe. Also I think since is a semi-historic manwha it represents really well what was the mentality until not too long ago

Because historically that is the situation in the far east? It wasn't a bunch of Han mandarins or Joeson yangbans living nomadically raiding the border villages on horseback. It was mongols and jurchens.
And even if we go full European setting, we're still dealing with Huns, Turks, and Mongols again.
They're depicted that way because that's who lived that way and so the shared image is them. It makes no sense to depict them differently.