Actually, Columbus was 100% certain the earth was round. What he believed is that the earth was significantly smaller than the mathematicians said, and that he’d be able to sail straight to India from Portugal. He was greedy and wanted to establish new trade routes. Most of the governments of Europe said "No, you fucking idiot, the earth is as big as the mathematicians say it is, and you’re going to starve to death on your way to India. They would have been right had he not bumped into America by accident. Anyway, that’s why native Americans are Indians and why there’s such a thing as the west indes.