What was the significance of the Dred Scott decision?
The Dred Scott decision was one of the incidents that helped to lead to the Civil War. It did this because it essentially made it impossible for the North and the South to make any further compromises on the issue of slavery in the territories.
In this case, the Supreme Court ruled (among other things) that Congress had no right to make any laws regarding whether slavery would be legal in US territories (at that time, territories were areas that were not yet states because they lacked the population). The status of slavery in the territories had been a major point of contention between North and South and had been somewhat solved by such things as the Missouri Compromise and the Compromise of 1850. With the Dred Scott decision, such laws became unconstitutional. Congress could no longer forge compromises on the issue. This mean that conflict was much more likely.
In that way, this decision helped cause the Civil War.