Answer:
1. The Abraham Lincoln-Stephen Douglas debates .
2. The Dred Scott decision by the Supreme Court .
3. Raid on Harper's Ferry by abolitionist John Brown .
Step-by-step explanation:
1. The seven debates between Douglas and Lincoln during the Illinois state election campaign (1858) included fundamental discussions to the sectional conflict about slavery and states’ rights.
2. Dred Scott v. John F.A. Sandford (1857) was a legal case in which the Supreme Court ordered that Dred Scott, a slave who had lived in a state where slavery was forbidden, had no right to freedom; that African Americans could never become citizens; and that the Missouri Compromise (1820) was unconstitutional. This ruling worsened the sectional dispute, in a path to civil war.
3. John Brown's raid on Harpers Ferry (1859) was an attempt by abolitionist John Brown to start a slave revolt that was defeated by the U.S. Marines, led by First Lieutenant Israel Greene.