It was a start. You have to realize that the world was not very civilized during the 1700s, especially outside of western countries. Many african slaves were sold go Europeans by other Africans who captured them. The western countries were some the first to outlaw slavery. "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness."
This quote from the constitution was a huge building block to end slavery in the US. You fail to realize that slavery wasn't always just black people and white europeans. There has been slaves of every color, hell slavery still exist today.