What would it take for Old World (Europe, Asia, and Africa) and New World (North and South America) to (mostly) remain uncontacted until the invention of human-controlled flight? Either heavier-than-air, internal combustion engine airplane, or lighter-than-air balloons or airships are okay answers for this challenge.
Obviously cross=straits contact by Arctic natives which was probably never absent for long can still happen, but civilitational temperate latitudes, population centers, information and knowledge networks are basically out of contact with each other unknowledgeable of each other until flight tech. Any exceptions are one-way travel or one generation, one-lifetime dead-ends (Vinland).
Obviously cross=straits contact by Arctic natives which was probably never absent for long can still happen, but civilitational temperate latitudes, population centers, information and knowledge networks are basically out of contact with each other unknowledgeable of each other until flight tech. Any exceptions are one-way travel or one generation, one-lifetime dead-ends (Vinland).