The Fugitive Slave Law required Northerners to assist in returning fugitive slaves back to their owners in the South. I put this first because it really brought about the topic of slavery in the North and also angered Northerners since they are free states.
Lincoln Douglas Debates
Bleeding Kansas describes what happened when the Kansas-Nebraska act was passed, which allowed popular sovereignty in Kansas and Nebraska. I put this second because this act violated the former Missouri Compromise since both states are above the 36°30 line, so they should be free states. This caused conflict between pro and anti slavery people, essentially creating a mini civil war in Kansas.
Election of 1860
Dred Scott sued for freedom on grounds that he lived in a free state. In this case, the Supreme Court ruled against Scott and said that Congress has no right to prohibit slavery in any territory and claimed African Americans living in the United States had no rights under the Constitution. I put this third because this decision made abolitionists feel that the Supreme Court was controlled by Southern "fire-eaters."
The Lincoln Douglas Debates were fought over the seat in the Illinois Senate. In these debates, Lincoln announced that slavery was morally wrong, the first politician to say their feelings on the topic. I put this fourth because now the anti-slavery people had a voice, and while Lincoln didn't win the seat, he did introduce new ideas.
In the Election of 1860, Lincoln was elected as president. I included this fifth because it brought up feelings from both the South and North. Since Lincoln was publicly anti-slavery, the South threatened to leave the union, but the North was happy for the representation.
The Missouri Compromise allowed Missouri into the union as a slave state and Maine into the union as a free state. From there on, if a slave state wanted to enter, they needed a free state to enter at the same time and vice versa to keep a balance. I included this sixth because it was a band-aid over a bigger issue and it later fell apart.