Jonathan Körner

One person responsible for making Florence a wealthy place was Cosimo de’ Medici who took over the family bank in 1430s. The Medici bank innovated in bookkeeping, debit-and-credit-accounting and by managing the fortunes of the wealthy, became wealthy themselves. Commercial development brought prosperity. Money and goods flowed into Italy from all around the world and Italy was rich. One of the factors that caused the Renaissance to happen in Italy was this wealth and patronage of wealthy people like the Medici. That was not it though. There was another important factor: the discovery of the past. The Tides of History podcast episode on the Renaissance takes a deeper look.
As the cities became wealthy, there was investment in art, education and architecture. The urbanized Italians, who had morphed into a society of ideas, had lots of questions on such topics and they found their answer in ancient Rome. It provided them guidance on education, linguistics and art, political ideology. There was a yearning for the past and it was a time of rebirth and the old was respectable because it was tried and tested before.
The Italians understood that there was a glorious past and then a fall. Roman concepts had stayed for more than half a millennia and was durable and reverence for the Roman past spread everywhere.  This rediscovery caused a cultural revolution and from Italy, it diffused into a wider Europe and freed Europe from its dark past into what they called Enlightenment. (But what they did was to enslave rest of the world and so European progress has to be seen with a huge sack of salt)
A new book on Leonardo da Vinci expands on the idea of the influence of the Roman past. Cosimo de’ Medici was schooled in Greek and Roman literature and was a collector of ancient manuscripts. Brunelleschi, an architect,. traveled to Rome and studied the classical ruins. They measured domes, studied great buildings and read the works of ancient Romans like Vitruvius. Leonardo studied Vitruvius and was fascinated by his detailed study of human proportions. This interest in the ancient past revived the writings of Pliny the Elder who praised artists who depicted nature accurately. The domes, realistic depiction of space, perspective, depiction of human forms — all were influenced by Rome.
Why did Renaissance happen in Italy and not elsewhere. It was not just wealth and the rediscovery of classics that caused the Renaissance to happen. There was a rediscovery of the ancient classics in the 9th century and later again in the 12th. But what made the 14th century rediscovery different was the depth and scale to which people went into the classics. Central and Northern Italy was urban. While there were only five cities with a population more than 40,000 north of the Alps, there were two with 100,000 in Tuscany alone There were many cities surrounded by the countryside. In the 9th and 12th centuries, only a tiny population was literate. Compared to that literacy rates in 14th century Italy was high. That produced a society of ideas instead of a small group of intellectual elite.
PS:  Lessons from the Renaissance for India