The Dred Scott v. Sandford decision angered Northerners because it declared that African Americans, whether free or enslaved, were not considered citizens of the United States and therefore did not have the right to sue in federal court. This decision also invalidated the Missouri Compromise of 1820, which had prohibited slavery in certain territories, and ultimately fueled tensions between the North and South over the issue of slavery and the rights of African Americans. Many Northerners viewed the decision as a major setback in the fight against slavery and a violation of the principles of equality and justice.
