The Revolt against England was a perfect time to try to bring about an end to slavery. Some of the delegates to the Continental Congress were opponents of slavery. Thomas Jefferson, who was himself a slave owner, seemed to understand the contradiction of writing a document stated: "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" and at the same, to hold slaves.
Jefferson wrote a line in one of his drafts of the Declaration of Independence that criticized England for allowing slave trade. In the end, the need to gain support for Independence trumped any concern about slavery. Jefferson's initial reference was eliminated, and nothing negative was said about slavery in the Declaration, whatsoever.