This is a really interesting article on HNN about Thomas Jefferson and Tadeuz Kościuszko. Kosciuszko wrote in his will that his estate was to be used to free all possible slaves (starting with Jefferson's) and that Jefferson was to carry it out for him. Kosciuszko wanted to give the slaves the opportunity to prosper. While Jefferson agreed to this will, once Kosciuszko died, he backed out:
Kosciuszko died on October 15, 1817. After several years of vacillation, Jefferson withdrew from his pact of honor with Kosciuszko by pleading in a Virginia court in Charlottesville that he could not serve as executor of his friend’s estate and would not use the money to free his slaves. As William Lloyd Garrison would say many years later, “What an all-conquering influence must have attended his illustrious example,” if he had taken the lead to abolish slavery.
And what happened to to the will and to Jefferson's slaves?
As Kosciuszko’s will, abandoned by Jefferson, made its way through the courts, many complications arose. The estate was finally awarded by the Supreme Court in 1852, 26 years after most of Jefferson’s slaves had been auctioned on the rolling lawn at Monticello to extinguish his debts, to Kosciuszko’s descendants. For years in Poland, Kosciuszko’s countrymen held the view that the American Civil War could have been averted if the Polish hero’s philanthropic, abolitionist plan had been implemented. When the slaves at Monticello mounted the auction block to be sold off after the Founding Father died—the slaves that could have been freed if Kosciuszko’s will had been honored—a small-town editor in a Susquehanna River town asked how Jefferson, “surely the champion of civil liberty to the American people,” left “so many human beings in fetters to be indiscriminately sold to the highest bidder."