For as long as English-speaking people have been settled in the US, there have been some who wish to put distance between the American version of the language and the type of English spoken elsewhere, especially that spoken in England.
Noah Webster is an example of a man who sought to earn respect for American English. He changed spellings and recorded words that were uniquely American. Many of them were loanwords from the Natives.
And then there was Washington J. McCormick, who argued in favor of making "American" the national language. The proposed bill did not make it far, but Illinois took a liking to it.
In 1923, Illinois officially declared "American" it's official language. Legislatures' reasons consisted mostly of a desire to see themselves as independent, not as an offshoot of England. Naming the language "American," they argued, would promote American culture, ideals, and institutions.
McCormick made the case that there had been great writers in American history, such as Twain and Whitman, whose greatness was owed to using language that reflected American usage. It was only when those authors quit trying to imitate foreign English-speakers and used an American style that they wrote their best.
