Elementary school teaches us the Declaration of Independence was originally written by Thomas Jefferson, who would later become the third president of the United States. What many textbooks are missing is: Jefferson's first draft of America's founding document included a harsh condemnation of slavery.

In the first draft of the Declaration, Jefferson criticized King George of Britain's support of slavery. From the document:

"He has waged cruel war against human nature itself, violating its most sacred rights of life and liberty in the persons of a distant people who never offended him, captivating and carrying them into slavery in another hemisphere, or to incur miserable death in their transportation hither. This piratical warfare, the opprobium of infidel powers, is the warfare of the Christian king of Great Britain. [Determined to keep open a market where MEN should be bought and sold.] He has prostituted his negative for suppressing every legislative attempt to prohibit or to restrain this execrable commerce [determining to keep open a market where MEN should be bought and sold]: And that this assemblage of horrors might want no fact of distinguished die, he is now exciting those very people to rise in arms among us, and to purchase that liberty of which he had deprived them, by murdering the people upon whom he also obtruded them: thus paying off former crimes committed against the liberties of one people, with crimes which he urges them to commit against the lives of another."

When Jefferson's first draft of the Declaration of Independence made it to the Continental Congress, many objected to the passage about slavery, and that section was removed from the Declaration on July 1, 1776.

This isn't the only time Jefferson spoke out against slavery, either. In 1778, Jefferson wrote a Virginia law that banned his home state from importing more slaves.

Yet, Jefferson's relationship with slavery is still being hotly debated.

Jefferson's relationship with slavery

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Jefferson's opposition to slavery may come as a surprise to some, because it's well known that Jefferson himself was a Southern slave owner. However, historians claim Jefferson did genuinely support the abolition of slavery.

"He was sincerely against slavery," John Boles, a professor of history at Rice University who has written about Jefferson, told ATTN:. "He just didn't know how he could end it for himself or for the nation, but he believed slavery was terribly wrong, and he spoke and wrote against it many times."

Boles said Jefferson was born into a slave society and inherited slaves, and he felt stuck in a difficult position. He did eventually free some of his slaves.

Annette Gordon-Reed, a professor of history at Harvard who wrote a book about Jefferson and his slaves called "The Hemingses of Monticello: An American Family," told ATTN: Jefferson was firmly against slavery.

"Jefferson certainly believed slavery was an evil," Gordon-Reed said. "He lost faith in his fellow Virginians' desire to do anything about the institution and concentrated on other things, namely the politics of United States of America."

You can argue his beliefs and his actions were sometimes miles apart. To this day there is an ongoing debate about Jefferson and his slave Sally Hemings, who many historians believe had six of Jefferson's children. A slave owner having sex with a slave constitutes rape by today's standards—particularly if she was underage. There remains some disagreement about what their relationship was really like, while others say it's wrong to conjure mitigating factors in sexual abuse that was common in slavery.

Gordon-Reed said that if Jefferson's words against slavery had remained in the Declaration, it may have had a major impact. 

"He has some pretty harsh words to say about the slave trade and he recognizes Africans as human beings in a very eloquent way," she said. "I think those words could've been used throughout American history had they remained in the Declaration."