A major change you should consider is the rise of towns and cities and the creation of the Middle Class, which had hitherto withered to insignificance in Europe. Medieval lords had encouraged peasants to become craftsmen, which many did. Craftsmen produced a surplus which could be offered for sale, and towns and cities developed near the walls of old medieval castles. Many were near roads and trade routes which accommodated trade. With the return of European soldiers from the Crusades, there was renewed interest in other products which bolstered the creation of a new class such as oranges, and especially sugar.
Three important demographic changes as a result of the development of cities and towns:
1. Those who lived in cities were freed men, no longer serfs. German historians used a phrase to describe this: Stadtluft macht frei. (The air of the city makes a man free.)
2. Tenants paid their rents to landlords by means of money rather than in labor or in kind as had been the case with serfdom.
3. Landlords normally guaranteed their peasants some protection from seizure of their property as long as rents were paid; otherwise tenants would not invest in the property. As a result, they enjoyed a degree of security not previously known. Although they were peasants, they were not serfs, nor were they nobility; they were somewhere in the middle, hence they became known as the "middle class."
This was by far the greatest demographic change. It should also be noted, however, that the return of the Crusaders which prompted renewed interest in trade with the East was the immediate forerunner and cause of the voyages of exploration which soon followed, which in turn were followed by the great Colombian Exchange.
Let's look at two major demographic changes from this time period.
First, there was major population growth caused by the "new agriculture" of the High Middle Ages. As agricultural practices became more efficient, more people could be fed. This led to a population boom. It is estimated that the population of Europe doubled from 1000 to 1300 CE.
Second, there was the disaster of the Bubonic Plague. The Black Death swept over Europe beginning in 1347. The epidemic killed huge percentages of the European population. It is hard to know for sure, but it is estimated that between a quarter and half of Europe's population died in the years 1347 to 1351.