History shows us this as well. It was after the Black Death in the 14th century that wiped out approximately 30% of the population of Europe at that time. (Historians please correct me if this percentage is incorrect!)
It was in the aftermath of the plague that the system in force at that time of serfdom was broken because there simply was not the abundance of labor anymore. This marked the rise of the middle class and the ability of free men to accumulate wealth.
What gave rise to the urban middle class was the population boom of the previous three hundred years. The Renaissance was in many respects a period in decline, because cause of the Turkish menace from about 1400 to 1700. The Portuguese and Spanish explorations were an effort to get around the Turkish monopoly in the eastern med. Accidentally they created a whole new whole new trading system.