The Dred Scott Decision was a landmark Supreme Court case decided in 1857. It involved a man named Dred Scott, an enslaved African American who sued for his freedom after living in free territories. The Court ruled that Scott was not a citizen and therefore had no right to sue in federal court. This decision effectively denied citizenship to all African Americans, whether enslaved or free. Additionally, the ruling stated that the federal government could not prohibit slavery in the territories, which heightened tensions between the North and South. The Dred Scott Decision is often cited as a significant factor leading to the American Civil War.