What replaced feudalism during the Middle Ages? How?

isaac newton first proposed that earth was not perfectly round. instead, he suggested it was an oblate spheroid—a sphere that is squashed at its poles and swollen at the equator.

the idea of the earth being a flat disc is also inconsistent with the fact that a given lunar eclipse is only visible from half of the earth at a time. the only shape that casts a round shadow no matter which direction it is pointed is a sphere, and the ancient greeks deduced that this must mean the earth is spherical.