What Stephen Douglas do before the civil war?

Before the Civil War, Stephen Douglas was a prominent American politician and a key figure in the Democratic Party. He served as a U.S. Senator from Illinois and was an advocate for the concept of popular sovereignty, which allowed territories to decide for themselves whether to allow slavery. Douglas is also known for his debates with Abraham Lincoln during the 1858 Illinois Senate race. Additionally, he played a significant role in the passage of the Kansas-Nebraska Act of 1854, which heightened sectional tensions over slavery.