Why was Lincoln upset by the dred Scott decision?

Abraham Lincoln was upset by the Dred Scott decision because it ruled that African Americans could not be considered citizens and that Congress had no authority to prohibit slavery in the territories. This undermined his belief in the principles of liberty and equality outlined in the Declaration of Independence. Lincoln saw the decision as a threat to the nation's moral and political fabric, as it effectively extended the reach of slavery and limited the possibility of its eventual abolition. He feared it would deepen the divisions between the North and South, escalating tensions that could lead to conflict.