"Instead of using our past to justify ourselves and inflate our collective ego, why don't we try to look at our past as a humbling lesson in just how much we have to live up to, on the good side, and how much effort we must put into breaking what of our destructive behavior patterns remain, on the bad?"

Our power has and will lessen relative to other nations- this because of US policy of free trade and technology of improving living standards and wealth throughout world.
But we have had a very destructive behaviour of discouraging DDT use in Africa- in this regard we have been almost as bad as the various socialistic states- something like 2 million people die horrible death from Malaria each year- plus many other suffer from the sickness and are permanently damaged by it. Plus it's drag on the economic growth of these countries [I think it's around 3% minus to economic growth]. But if you just counts deaths and start from say 1970 [a period we could have done something about it] that's about 70 million dead. That's getting up to Stalin level- though it's from neglect and stupid ideas [psendoscience] rather direct purposeful cause [murder/genocide/forced labor death camps].