Clarificaion please

‘We hold these truths to be self evident: that all men are created equal; that they are endowed by their Creator with certain inalienable rights; that among these are life, liberty, and the pursuit of happiness’

It seems a bit queer, as in peculiar, that, as I’m informed, the above words are regarded to be a part of the most important document in American history. Furthermore, they are the over-arching guiding principle of subsequent documents such as the Bill of Rights. If the above wasn’t valid, then what inspires the rights etc.? Yet, as I watched the film ‘Lincoln’, and the arguments it floored for a 13th amendment, it was contended that former slaves could only be equal in the law (presumably the producers did their homework). If so, then doesn’t that mean that the declaration doesn’t apply to all ‘men’? Or are African Americans not ‘men’ under the principles of the above? IF so, then does that mean that the principles of equality and the pursuit of happiness do not apply to all American citizens?

Given the current problems we witness on our TV’s almost daily regarding issues of colour (allow me to translate – ‘color’) in the U.S., could this blurriness be a part of the root of both problem and solution?