I'm not British so I'm unlikely to denounce them the way someone from the UK might. And I would add that Washington, et al, were motivated enough by their cause to win their rebellion. Lee, et al, were not. Winning changes a lot of things.
Lee, et al, were not.
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Defeat does not necessarily denote lack of motivation. The Confederates were — in the end — outgunned, outmanned, and — the killer — out-technologied. I think the number of battles where smaller Confederate forces out-fought their more numerous Union opponents weakens your proposition considerably. Though some Southern leaders wanted to continue with a long-term guerilla war, Christian compassion ruled that out for many Southern leaders.
You are correct: Winning changes many things — but not the facts. Only those who get to teach their interpretation of the facts in Government schools. But this is your strongest argument, yet.