What is the origin of the term "chip on your shoulder"?

Search: chip on your shoulder origin

Why: Keira Knightley said:

Not going to university did give me an incredible driving force because it leaves you with a slight chip on your shoulder.

Answer: It is American, first recorded in the Long Island Telegraph for May 20, 1830:

When two churlish boys were determined to fight, a chip would be placed on the shoulder of one, and the other demanded to knock it off at his peril.

The same idea is mentioned in the issue of The Onondaga Standard of Syracuse, NY, for December 8th the same year:

“He waylay me," said I, "the mean sneaking fellow — I am only afraid that he will sue me for damages. Oh! if I only could get him to knock a chip off my shoulder, and so get round the law, I would give him one of the soundest thrashings he ever had."

Source: World Wide Words

The More You Know: And from Phrases.org.uk, in James Kirke Paulding's Letters from the South, 1817:

A man rode furiously by on horseback, and swore he'd be d----d if he could not lick any man who dared to crook his elbow at him. This, it seems, is equivalent to throwing the glove in days of yore, or to the boyish custom of knocking a chip off the shoulder.

I wonder what "d----d" means.