Maybe this is too close to a "what if", but what I'm really wondering about is the general angle of European exploration in the time period. Suppose Columbus doesn't ever try to sail west (for simplicity's sake, let's say he never personally proposes the idea at all). How long would it have taken someone else to try the same thing? Presumably something like Magellan's attempt to circumnavigate the world would have resulted n finding the Americas, but would that have been attempted without European presence there?