Democratic New York Rep. Alexandria Ocasio-Cortez made a false claim involving Washington D.C. and slavery while making the case that the District of Columbia should be a state.
In reality, Vermont became the first U.S. territory to abolish slavery in 1777, and Pennsylvania was the first state to officially end the practice in 1780. Washington D.C. was not officially a territory until 1790.
Washington D.C. was actually one of the last territories in the U.S. to abolish slavery. The slave trade ended in D.C. in 1850 as part of the Compromise of 1850, and it officially became illegal to own slaves in the district in 1862 after the passage of the D.C. Emancipation Act.