The second to last huge population decline was the Black Death. The loss of population made labor scarce, frayed the knot the feudal system had on people, event

The second to last huge population decline was the Black Death. The loss of population made labor scarce, frayed the knot the feudal system had on people, eventually resulting in increased mercantilisme, urbanisation and ultimately The Renaissance. The first, was of course, The Great Dying of the Americas. So things really could go either way.