When George Washington died in 1799, a new nation ground to a halt. Mourning Americans wore black crepe armbands. Church bells tolled. And at Mount Vernon, the first president’s estate, wrote a visitor, “Every one was affected, but none so much as his domestics of all ages.”

Or so the story goes. Washington’s “domestics” were enslaved workers. And though he promised in his will to free all of his workers when he died, only one of them immediately went free and nearly half of the enslaved people at Mount Vernon remained in bondage for decades. The reason why has to do with law, marriage and a family that disagreed with their patriarch’s evolving views on slavery.

Like nearly all wealthy landowners in Virginia, George Washington owned enslaved people who worked his land. He received the first enslaved workers of his own when his father died in 1743. Washington, just 11 years old at the time, was willed 10 enslaved people, and by the time he married Martha Custis in 1759, he had purchased at least eight more.

His new wife was a 25-year-old widow who arrived with enslaved workers of her own. At the time, a young woman’s father was expected to provide a dowry, a gift of money, land and other assets, to her new husband. If he died before she did, a wife was entitled to one-third of his estate, also known as a “widow’s third” or a “dower share,” throughout the remainder of her life. She would live off of the proceeds of her dower share and when she died, the money and assets would revert back to her late husband’s heirs.

The dower share was designed to protect a woman from poverty if she became a widow, but even though it was technically hers, it immediately became her husband’s to manage when she remarried.

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Martha’s dower share was massive and made her into one of Virginia’s richest women. When her late husband, Daniel Parke Custis, died, two-thirds of his assets automatically went to their eldest son, John, who was a minor. The other third—including enslaved people—later went to Washington to manage. The enslaved people and all of their children were considered part of the dower share, and though they lived on Washington’s estate and served him, they were technically held in trust for Martha’s children. When they married, Martha brought 84 slaves along with her.

By the standards of his day, Washington treated his enslaved workers better than most. But he expected more from them than the average slave, especially as he began to use his plantation as a kind of efficiency experiment. The future president tried out new farming techniques, closely monitored his enslaved workers’ production in connection with the farm’s yield. He whipped, beat, and separated people from their families as punishment. Washington also relentlessly pursued escaped slaves and circumvented laws that would allow his enslaved workers freedom if they did manage to escape to neighboring states.

Over the years, Washington’s thinking on slavery evolved. During the Revolutionary War, he became more uncomfortable with the thought of purchasing and owning other human beings. But though he supported abolition in theory, he never tried it in practice. His plantation, his wealth and his position in society depended on enslaved workers. And, as noted in Erica Armstrong Dunbar’s book, Never Caught: The Washingtons’ Relentless Pursuit of Their Runaway Slave, Ona Judge, when one of Martha’s enslaved workers fled to freedom in 1796, Washington spent the last three years of his life trying to force her to return.

In the words of historian Henry Wiencek, his contradictory attitudes towards slavery are “one of the mysteries of his life.” Those contradictions made it into his will, too. Though the will contained the unheard-of order to free his enslaved workers, it stipulated that they remain with Martha for the rest of her life.

Freeing them, he wrote, would “be attended by such insuperable difficulties by their intermixture with the dower Negroes, as to excite the most painful sensations…to manumit them.” Translation: It would be too complicated to free the enslaved people, so instead they would be owned by Martha as long as she wished.

Since he didn’t technically own the enslaved people Martha had inherited, he didn’t say they should be freed. Instead, he used them to justify the continued enslavement of the others.

By the time George died, he owned 123 enslaved people outright. After Washington’s death, Martha freed just one person: William Lee, a Revolutionary War celebrity who was the only enslaved person George said should be immediately given his freedom. But she didn’t free the others—until she became convinced that they were plotting against her.

READ MORE: The Massive, Overlooked Role of Female Slave Owners

After at least one fire and a rumor that an enslaved person wanted to poison her, she freed the rest of George’s enslaved workers about a year after his death. It was just too risky to keep “restive” enslaved people who longed for freedom among those she had inherited, she implied to friends like Abigail Adams.

But was that really the reason? Historian Marie Jenkins Schwartz suggests that Martha’s real motivation was financial and that she felt taking care of her husband’s enslaved workers was leeching money from her children’s estate. Either way, freeing George’s enslaved workers wasn’t as complicated as the president implied in his will. In January 1801, they left Mount Vernon as free men and women.

The 153 enslaved people who Martha had inherited weren’t so lucky. They were divvied up between her children when she died in 1802. None of Martha’s children freed more than a few of the enslaved workers or their children during their lifetimes. And Martha never freed the single enslaved man she owned outright, even willing him to her grandson. George’s views on slavery may have been advanced, but his family apparently did not share them.