What are the historical significance, background, and evolution of the words to the song Maple Leaf Rag by Scott Joplin?

When examining the lyrics to Scott Joplin's classic ragtime composition Maple Leaf Rag, it is important to keep in mind that the lyrics were written some time after the 1899 publication of Joplin's original music, and not by Joplin. Rather, the lyrics were penned by Sydney Brown. Brown's lyrics, which were added with or without--probably the latter--Joplin's consent by his first publisher, John Stark, who had acquired the rights to Maple Leaf Rag and with whom Joplin had an ongoing feud, were noticeably racist and perpetuated negative stereotypes of African Americans. 
Ragtime was a product of late-nineteenth-century America and, more specifically, of the American South. As with blues and jazz, to which ragtime was a precursor, this musical genre was unique to the African American community, in particular those in St. Louis and Sedalia, Missouri. The origins of ragtime, then, cannot be separated from the racial hostilities and institution of racial segregation that continued to plague the South for decades after the end of the Civil War. And, in contrast to some other ragtime composers, Joplin eschewed music that catered to the lowest common denominator of white American society. The publication by Stark of Brown's lyrics, consequently, do not reflect upon Joplin, but upon the racism endemic to society during the latter's life. Ray Argyle, in his history of ragtime and of Joplin's role in popularizing it, Scott Joplin and the Age of Ragtime, quotes the American Federation of Musicians' 1901 declaration that "swore to play no ragtime and to do all in their power to counteract the pernicious influence...of the Negro school." (p. 36) Such was the atmosphere in which Brown penned the lyrics to Joplin's composition.
The lyrics to Maple Leaf Rag are replete with negative imagery illuminating the racial prejudices of the time:

I came from ole Virginy from the county AcomacI have no wealth to speak of 'cept de clothes upon my backI can do the country hoe-down I can buck and wing to show downAnd while I'm in the notion, just step back and watch my motion
Oh go 'way man, I can hypnotize dis nationI can shake the earth's foundation wit' the Maple Leaf Rag
..
The men were struck wit' jealousy, the razors 'gan to flashBut de ladies gathered 'round me for I'd surely made a mash
The finest belle, she sent a boy to call a coach and fourWe rode around a season 'till we both were lost to reason....

Note the use of phrases like "de clothes," "I can buck and wing," "I can hypnotize  this nation," and "I can shake the earth's foundation wit' the Maple Leaf Rag." Brown's lyrics tell of a poor African American walking into a presumably upper-class white dance and scandalizing the attendees. Among the pernicious stereotypes of African American men was that they were sex-crazed predators who targeted white women. When the singer suggests that he can "shake the earth's foundation," he is playing to the fears of many caucasians that blacks were innately threatening not only to the status quo but to the sanctity of white women. The reaction of the men in the ballroom further perpetuates the myth of the ever-threatening African American and, of particular note, of the white man's need to castrate the black man who will otherwise rape white women with wanton abandon.
Sydney Brown's lyrics for Scott Joplin's composition are rarely heard for the simple reason that they do not improve the music and are highly offensive. They represented a bastardization of Joplin's music while also illuminating the blatant racism of the era in which both the original composition and the lyrics were written.
http://www.perfessorbill.com/lyrics/lymaple.htm