How did slavery conflict (go against) the principles of the declaration of independence?

According to the Declaration of Independence, every human being living in the United States has the right to be free and decide its own ways in life, and than on the other hand we have the slavery, where people were enslaved, were either slaves for all of their lives or occasionally they were able to buy out their freedom, and they did not decided for their own lives but their owners. These two are the two total contrasting opposites that occurred in the American society, and they show how it is possible that from one negative extreme, the country can be reformed and functioning in another positive extreme.

the  wilmot proviso  was designed to eliminate  slavery  within the  landacquired as a result of the mexican war (1846-48). fearing the addition of a pro-slave territory, pennsylvania congressman david  wilmot proposedhis amendment to the bill.

19th amendment granted women the right to vote. the 19th amendment guarantees all american women the right to vote.