Two very significant pieces of legislation that helped lead to the Civil War were the Fugitive Slave Act of 1850 and the Kansas-Nebraska Act of 1854. The Fugitive Slave Act required Northerners to return escaped slaves, sparking outrage in the North, even from people who had not cared much about slavery previously. The Kansas-Nebraska Act applied the principle of popular sovereignty to newly opened territory in Kansas, which led to tremendous violence as pro-slavery and anti-slavery forces fought for control.
The two signal political compromises were the compromises of 1820 and 1850, which, while too long to discuss in the context of this question, attempted to resolve the issue of the expansion of slavery into new US territories and states through compromise measures, including the Fugitive Slave Act. It is enough to say that these extraordinarily complex packages of compromise legislation forestalled, but could not avert an eventual showdown over the issue.
The most important Supreme Court case was Dred Scott v. Sandford (1857), in which the Supreme Court ruled that slavery could not be banned in the federal territories, and that not just slaves, but black men in general had no rights that white men had to respect. This case reinforced the sense in the North that a "slave power" controlled the federal government, and through its machinations was using federal power to push the institution down the throats of whites.
Finally, the presidential elections of 1856 and 1860 were paramount in bringing about secession and civil war. The election of 1860 is important for obvious reasons, because it was as a result of Lincoln's election that the Deep South states seceded from the Union. But it was the 1856 election, which brought James Buchanan into office, that revealed the extent to which the nation was divided. The old Whig Party had shattered under sectionalist tensions, and the new Republican Party, which drew support only from the Northern states, emerged as a national force.