The United States' legacy? Why not our inventions - the light bulb, the semiconductor, or the airplane? Or the leaps in civil rights, through government of, by, and for the people? We were one of the first nations to outlaw slavery. We're the second-oldest continuously-functioning government on the planet, and the oldest republic.
Those are things people will remember 500 years from now. The advertisements for Coca-Cola? Not likely.