One of the most significant happenings of the Medieval period that paved the way for the Renaissance was, ironically, the Bubonic Plague, also known as the Black Death. The plague started in Asia and swept through Europe beginning in 1347, reducing the population of Europe by as much as a third. This caused a labor shortage in agriculture and gave peasant tenants leverage to demand higher wages and lower rents from their landlords. Landlords often refused, and this gave rise to peasant rebellions. The late Middle Ages was a period marked by social rebellion—an important factor in setting the stage for the Renaissance.
The commercial class—traders, merchants, shopkeepers, and artisans—began to grow and prosper in towns and cities. These workers were socially above the farm-laboring class but below the nobility. The members of the commercial class tended to be individualistic in their goals and focused on the success of their businesses. They began to break with the tradition of almost total reliance on the Church for guidance. Though religious people in the commercial class began to focus more on their daily lives than on the afterlife and became more open to information that came through with trade.
Cities in northern Italy, such as Milan and Florence, became very prosperous through the work of the commercial class and through manufacturing. The location of the northern Italian cities was ideal for trade with Asia, Africa, and the rest of Europe, which allowed for the flow of new ideas. The rise of individualism and the intellectual cross-pollination that took place with exposure to new ideas, as well as renewed interest in the Greek and Roman classical works of literature, art, and philosophy, also helped to create the Renaissance.
Another important development in the transition from the Middle Ages to the Renaissance was the rise of independent Italian city-states that had formed as people began to free themselves from the controlling powers of feudal landlords. At one point, there were 250 city-states in Italy. Florence, a key city of the Renaissance, was ruled by some 800 of the city's wealthiest families. The ruling families (often made up of aristocrats, merchants, and bankers) were patrons of the arts and sponsored architects and artists to beautify their cities and enhance their reputations—making it financially possible for geniuses of the era, such as Leonardo da Vinci, to pursue their creative endeavors.