Why were the mongols able to build a much greater empire then their nomadic predecessors?

The Mongols greatest strength was the incorporation of the technologies and ideas they learned as they expanded their empire. Most importantly, their use of Chinese engineers to build bridges over rivers and the use of gunpowder. Also the Mongols learned administration skills from the Chinese and the Persians. You can't build an empire with just an army, you need to insure that commerce and trade grows, roads and bridges have to be built, people must be free to prosper, and of course taxes must be paid. These ideas they learned. And with it their empire grew.