Another major factor in our Revolution's success was the involvement of the French and Spanish.  Yorktown would never have happened without a French naval victory.
In an agrarian society, guerrillas are fine except at planting and harvest time.  We had some problems there.  And we had home field advantage.  The British had a long supply and logistics line to maintain.  There was also a certain amount of sympathy for the American cause back in Merrie England.
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Geezer in Chief