It was primarily the "Open Door Policy" that opened relations between china and the united states, since this made it possible for many western countries to engage in trade with China.
The main factor regarding the <span>United States dominating the world economy after the world war 2 was that it was a highly industrialized nation, and had not been "touched" by the war physically due to its isolation between two major oceans. </span>
I believe the flag should stay up because that memorializes the Civil War and the whole receding from the U.S.
