Florence was the birthplace of the Italian Renaissance. Politically, economically, and culturally it was just about the most important city in Europe for something approaching 250 years - from sometime before 1300 until the early 1500s.
Florentines reinvented money - in the form of the gold florin - which was the engine that drove Europe out of the "Dark Ages" a term invented by Petrarch, a Florentine. They financed the development of industry all over Europe - from Britain to Bruges, to Lyon, to Hungary. They financed the English kings during the Hundred Years War. They financed the papacy, including the construction of Avignon and the reconstruction of Rome when the papacy returned from the "Babylonian captivity".
Dante, Petrarch, and Boccaccio pioneered the use of the vernacular - the use of a language other than Latin, in their case, Tuscan, which, because of them, became Italian. Because Dante, et al., wrote in Tuscan, Geoffrey Chaucer - who spent a lot of time in Northern Italy and who stole Boccaccio's little stories - wrote in English. And others started writing in French and Spanish and so on. This was the beginning of the end of Latin as a common language throughout Europe.