Dred Scott v. Sandford was a landmark Supreme Court case decided in 1857. The case involved Dred Scott, an enslaved African American man who sued for his freedom after living in free territories. The Court ruled that Scott could not sue because he was not considered a citizen under the U.S. Constitution. The decision further stated that the federal government had no authority to regulate slavery in the territories, effectively invalidating the Missouri Compromise. This ruling intensified national tensions over slavery and contributed to the events leading up to the American Civil War.