This is silly,
The Americans joined the war because of Pearl Harbour (which stifled the isolationists) and we were very happy that they did. American intervention did win or shorten the end of both wars.
...and Lasz is right about the Red Indians, their fate was inevitable, as has happened in cultures before them.
It would be nice to live in a world where there was no change and people were in harmony in their environment (as the red indians were) but as with Africa, for example, we introduced them to advanced weaponry and after an untold number of deaths we are only now just waking up to the cost.
It's very hard to apportion blame in such circumstances.
Ravs