Well since the formula requires a victory, let us forgo any discussion of principle. We should just resign all that flowery talk about the rights of the people to the garbage heap where it belongs. If you have the power to enforce your will, then you are in the right. Eh, but isn't that a bit like slavery?
The 13 colonies met that standard. The slaveocrats did not.
England could have won. They chose not to continue killing their former countrymen. Had an obsessed man sat on the English Throne, the Colonies would have fared as badly as did the Confederates.
George III was that obsessed man and would have continued the war if it were his choice. His Parliament said enough is enough. They could no longer afford the fight and had more pressing problems in Europe. (Aside from the fact that most of the Tories in Parliament sympathized with the American cause.)
It was the first time the British Empire ever gave up colonies. The last time was nearly 200 years later.