"In Washington DC it was illegal to own slaves after 1850. So if a slave owner, or a Foriegn Diplomat, moved to Washington, the United State would free the slave pay the master $100 and ship the exslave to Liberia, North Africa."

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Slavery was not formally abolished in Washington DC until 1862, during the Civil War. The Compromise of 1850 outlawed the slave trade in DC, but did not outlaw the institution itself.