Until they established city centers, trade routes, spread religious freedom to among their subjects, developed population centers and their agricultural output, standardized exchange rates and quality bars, created systems of news and material delivery, and all that other stuff.

Their empire was, of course, extremely short, as it collapsed with the death of their Great Kahn soon after it established itself and its following leaders abandoned the previous inroads in the West to focus on the prize of capturing China (that ultimately failed).

Our history tends to focus on the expansion of their empire rather than its subsequent administration, I think in part for that reason.

They didn't raise crops, but still practiced a considerable amount of agriculture based around grazing herds.

And raising horses, nomad's still practice agriculture.

I suppose so, I forgot western civ was one battle loss away from not existing as a continuous entity. So yeah, military only seems to be possible, even if the Mongols were not 100% faithful to this strategy, I think someone could have been successful.