I've asked that question before and the general consensus seemed to be that Webster just grabbed control. If I spell color "colour" on a spelling test, I'd be marked wrong. But why? I imagine in the 1700 when US was still a British colony that we spelled it colour. At what point did somebody say it will now be spelled "color"? Who gave them the authority to do this? And if this never officially happened, but was just a result of the populace preferring that spelling then what right would a teacher have to mark a student off for that spelling. And why wouldn't "phone" become "fone" now that everyone texting their friends on their cell phones have popularized the spelling?

Although I'm not aware of an authorit for the English language, I've been told that the Spanish language does have an overseeing authority.