Louisville's location as a major river port made it one of the most important trade hubs in the early years of the United States. Agricultural goods and trade good moved down the river towards the Deep and Upper South. Agricultural growth caused a population boom in the area, but also had a darker result. Kentucky's slave population grew. By the 1820s, 26% of the state's population were slaves.
With this excess slave population, Kentucky began exporting their slaves to other slave states down the river to New Orleans. This is also the rise of phrase "being sold down the river". Through the 1850s 2500-4000 slaves were traded from Louisville slave pens; by 1860 the slave population in Kentucky had shrunk to roughly 7%.
Louisville's position also made it an important part of the Underground Railroad which helped slaves to get to free states. If they could cross the Ohio River into Indiana, they could make their way to freedom. However the journey was risky, as slave catchers often were constantly looking for escaped slaves.
When the Civil War broke out, Kentucky was the only slave state that stayed in the Union that did not outlaw slavery. That being said, roughly 75% of the state's slaves were either freed or escaped to the Union lines during the course of the war. Slavery was abolished with the war's end in 1865; however the state of Kentucky did not ratify the Thirteenth Amendment--officially ending slavery in the state--until 1979.