Has anybody mentioned the Ottomans? Think about it: nomads from Central Asia make their way to Anatolia, remaining for the most part a series of competing tribes without being destroyed. They then proceed to not only conquer Anatolia, they cross into Europe without taking Constantinople. All of this is done while surviving the entrenched local powers and Timur, who kicked their asses. After beating every major power in the region and conquering a city renowned as an impregnable fortress, they drive deep into Europe through the terrible infrastructure and besiege Vienna and drive off a coalition that formed to stop them, retaining massive gains. And as they decay, they still retained massive territories despite being outclassed. On top of that, in their penultimate war they not only stand up to the world's greatest power, they bloody its nose and deny it victory on the battlefield, forcing it to rely on internal revolt. They then defeat an attempt to carve up Anatolia by the victorious powers before finally becoming a republic. And remember, this was done by nomads from Central Asia.