Why has the U.S. turned over many National Parks and Monuments over to the United Nations?

Who created the World Heritage Sites? Why are we allowing the U.N. to have control of any part of our country? Who’s idea was it to allow this? Are U.N. Funds used to maintain these sites? And how do you, as an American, feel about this?

World Heritage Sites were determined by the United Nations to which the member countries adhered for the protection of the sites.