When did yuan officially come into existence​

In 1271, Kublai formally claimed the Mandate of Heaven and declared that 1272 was the first year of the Great Yuan () in the style of a traditional Chinese dynasty.

Unless that’s a typo and you meant UN
In which case the answer is 24 October 1945

Michigan cannot ignore the us constitutionboth constitutions contain the same fundamental ideas

The answer would be hard press.