I still maintain, how can you "discover" a place that has inhabitants? Methinks some group of nomadic Mongols discovered North American many centuries before either one of these guys on a landbridge through the Bering Sea.
Because those who were there didn't know where they were. They had no maps and no conception of the outside world. It's not a mere matter of existence.
Things have changed in the world of sovereignty and stateness since then. At that time Columbus was legally entitled to claim the New World for Spain. The people who were here already had no claim since they could not refute the Euro claim. European rules were the rules of the day.
It is well known that Eratosthenes was the first to accurately estimate the Earth's diameter, around 220 BC. It was also a well known fact in 1492.