People and empires were on the move during the years of the MWP, and they stopped moving-or moved out-afterward.  SOMETHING was certainly happening at this time, and something destroyed many of these great empires. 

When the Maunder Minimum struck in 1645, the Earth appears to have cooled globally, and the moment in the sun for many great peoples and kingdoms ended in the darkness of a cold, hungry world. Only the Europeans, who by then were in the midst of THEIR expansion into the world at large, had the tools to take advantage of the situation, and thus Europe colonized the world. Indeed, they likely HAD to colonize the world, or else slide into that abyss reserved for those many civilizations that have passed from our collective memory.

And thankful we should be that the land once known as Christendom did not fade as these many others. Their day in the sun is past, and the coming of the cold wrecked their once proud kingdoms. A warm world is hardly a bad thing.

Here.