Several people posting on this board have endorsed defense of 'States Rights' as the cause of secession and the Civil War. In their version of events, abuses of 'States Rights' by the U.S. government and encroachment of Federal power over the states compelled Southern citizens to seek a remedy in secession and formation of an independent country. Even though delegates to the new nation’s constitutional convention adopted significant revisions defending the rights of slaveholders, we are told that slavery was a negligible issue which did not really drive secession.

In fact during the years leading up to the Civil War, ‘States Rights’ was endorsed by citizens of Northern states, specifically by people opposed to slavery and the rights of slaveholders. Republican legislatures enacted Personal Liberty Laws, which forbade state law enforcement officials from enforcing the U.S. statute on Fugitive Slaves. Of course this position was identical to that held by the State of South Carolina twenty-five years earlier when Andrew Jackson overturned Nullification.
http://www.econlib.org/library/YPDBooks/Lalor/llCy820.html

Here’s an example of ‘States Rights’ support from the State of Wisconsin, with italics placed for emphasis.

Early in 1857 the new legislature adopted a “personal liberty law” prohibiting state officials from assisting in enforcement of the federal Fugitive Slave Act. It also submitted a referendum on black suffrage to the voters at the November election. In Milwaukee, on June 17, a mass meeting of confident antislavery Republicans greeted with “hearty applause” speeches by the abolitionist Gerrit Smith and John Brown. Among the resolutions approved by the audience, one denounced the “alarming encroachments of the Slave Power” and deplored the Dred Scott decision, which nationalized slavery and denied free blacks the rights of citizenship. Another reaffirmed the duty of Congress to prohibit slavery in the territories but challenged its authority to legislate for the recovery of fugitive slaves. Still another, in an assertion of states rights, noted that the Wisconsin Supreme Court had ruled the Fugitive Slave Act unconstitutional; therefore, whoever seized a fugitive in the state would be guilty of kidnapping. Finally, the meeting resolved that, “as slavery is a crime against humanity . . . it can no more be constitutionlized or legalized, than theft, murder or robbery . . . .

Kenneth M. Stampp, America in 1857: A Nation on the Brink, p. 254, quoting the Milwaukee Sentinel, June 29, 1857, and Current, History of Wisconsin, vol. II, pp. 260-262.

Note popular support for Gerrit Smith and John Brown, both involved in the Harpers Ferry conspiracy of October 1859.

Isn't it curious that Republicans in Northern states believed slavery to be the source of the conflict with the South? Too bad they couldn't understand that Southerners weren't really interested in slavery; after all, people in the South supported ‘States Rights’ too! ;-)