What caused the renaissance to begin?

The great plague cause the renaissance to begin. Since in some places up to 50% of the population had died, all the resources were now split among the survivors. There was more resources to invest in art and culture. It took half the fields to feed people, so the extra fields were used for specialties like tomatoes, olives, and the like, resulting in new cuisine. And modern science was born from the realization that the superstitions of the day were not enough to understand our world.