Imagining the unimaginable

I will admit right up front I have not seen this film. This is my answer to DD's challenge to imagine a world without the U.S.(I am assuming that is what DD is referring to since America as a place would have existed without the U.S.).
I take it (from the reviews I have read) that DD has Washington being killed in the war and takes it from there. I would like to go even further back and posit this: King George the 3rd agrees to and does rectify the conflicts between the Crown and the colonists, and the Revolutionary War does not even occur. So what could realistically be expected to have happened?
Well, we really need look no further than our neighbor to the North, Canada. They have a well established Parliamentary democracy independent (for all intents and purposes) of the Crown. Canada is a member of the British Commonwealth, along with several other democracies such as Australia and New Zealand. They are all peaceful, prosperous countries who view with no small amount of pride their membership in the Commonwealth. It is entirely reasonable to believe that the American colonies would have followed the same path. Perhaps they may have formed a union that became preeminent in the Commonwealth, but that union would still be a member.
Now admittedly, the world would be lacking some superlative and moving documents expressing humanity's desire for freedom, but on the other hand Native Americans may have been treated much more humanely, slavery would not have been enshrined in the Constitution, and the casualties of the Revolutionary War, the War of 1812, and the War between the States could have been avoided. And as to the role of the U.S in World Wars 1 & 2? The resources which enabled our contributions would still have been available, only we would have been fighting alongside our fellow Commonwealth members.
Of course, all of this is moot. We have our history and it cannot be changed. I am proud to be an American and of the contributions we as a people have made to the world as we know it. But it is a pride tempered by the realization that we have made tremendous mistakes as a nation, mistakes which have cost us and other nations dearly. For anyone to make the claim that the existence of the United States is somehow indispensable just does not hold up to scrutiny.