And the King said no way. We had to win a long, bitter war to make it a reality.
And this argument simplifies to "Might makes right", which is, I believe, an accurate assessment of what happened.
King George had the power necessary to win. What he lacked was the will to do so. So our great founding, rather than being a matter of principles in which we claim to believe, simply comes down to a matter of a lack of will power on the part of the British Chief executive.
Had Lincoln been in charge, we would all still be singing "God Save the King."