Mouzafphaerre is right tho, while they excelled at defeating the armies of other nations, because of their nomadic nature as soon as they settled down to ruling, not conquering, they slowly but surely stopped being mongols, and became a minority group (ruling minority in china for a while) who eventually just became another part of the cultuire they had defeated.

The chinese were perticularly good at this, while I don;lt recal the exat dates and such they were invaded and conquered several times, and ever time the invaders slwly became a part of the chinese culture, rather than replacing it. This is on part because they were so advanced for the tiem, but also because they didn;t seem to mind being conquered, taxes might be high for a while and the rulers change, but the people carry on doing what they had been for years before, no matter who says they are in charge.

As for mongols ruling, well, if ghengis had carried on west, the roman empire would have fallen before him, that is very likely, and the pope would not have susrvived, at least not as the pope, but the mongols would soon have been learning latin, living in houses rather than huts and the glorious mongol empire would soon have been nothing more than a memory. yes, the implications on russia would have been dire, but even they would have probably absorbed the culture of the mongols into their own, and long term changes would have been slight.