Was thinking about various factors that influenced the discovery of America – by which I mean Columbus’s voyage. Not Saint Brendan or Madoc, not the Phoenicians, not the Romans, not the Solutreans. Not Basque fishermen. Not Leif Ericsson or Bjarni Herjólfsson either, because, although they really did get there, the information didn’t spread far. The same for Polynesian contacts – they did visit South America, but since they themselves were isolated from the Old World, it didn’t go anywhere.
First, they had cheap, reliable ships that were up to the job. I emphasize cheap.
Columbus and European civilization _knew_ there was land on the other side – China, if nothing else. They knew the world was round. Unfortunately for Columbus, potential backers also knew how _big_ the world was, and how very far it was to China ( he had a fruitful delusion about this.)
One factor must have been the discovery of a number of useful islands in the Atlantic: the Azores, Madeira, the Canaries ( rediscovered, really – already inhabited and known to the Romans). An expedition that merely found another Madeira would have more than paid for itself. Legend placed plenty of other islands out in the Atlantic, from Antillia to Huy-Braseal.
Could Columbus have known about Leif Ericsson and Vinland? Just barely possible: there were people in Iceland that remembered Vinland, but the story wasn’t generally known in Europe. And even if he had heard, he was going far south of their discoveries.
People have occasionally wondered if sea beans had something to do with it. Sea beans, or drift seeds, at least the ones we’re interested in, are buoyant seeds come from tropical plants in the New World. They can float long enough to reach the shores of Western Europe. When you found a sea-heart on the beach, something that clearly did not originate in Europe, surely that unknown land felt a bit more real.