What happens if the Ming Dynasty China decided to conquer Mongolia and annexed it, rather than going on the defensive in OTL? How would they be able to accomplished it?

How would it impact on the world where Mongolia is conquered by the Ming Dynasty earlier than the Qing?

The time will be around the reign of Hongwu or his successors.
Lots of hell. I don't think the Ming would bother as much to pacify them, as the Qing had. Most likely, they'll leave behind a puppet khan and obtain tribute.

If they did try to pacify the frontier, well, let's just say it'll be difficult and expensive. The Imjin War sapped the by-then flagging Ming economy to breaking point, opening the way for the Qing conquest. What's to say trying to tame the Mongols was going to be any easier. :v

Impact-wise... Depends on what they do? Colonization by the Han would likely result in something resembling OTL's Inner Mongolia, with the Mongols reduced to a minority. But the steppes aren't exactly prime real estate...