What was the first battle between those favoring the extension of slavery?

The first significant battle between those favoring the extension of slavery and their opponents was the Battle of Lawrence, fought in May 1856 during the Bleeding Kansas conflict. This battle emerged from the violent struggles between pro-slavery forces, known as "Border Ruffians," and anti-slavery settlers who were moving into Kansas to establish a free state. The clash in Lawrence marked a pivotal moment in the escalating tensions over slavery in the United States, foreshadowing the broader national conflict leading up to the Civil War.