The Free Soil movement contributed to the Civil War by convincing Southerners that slavery was under threat by the North. The phrase "Free Soil" referred to the demand that slavery be restrained to its current borders (i.e., that the institution should be banned from spreading into Western territories and states). This followed the principle of the Northwest Ordinance, which had closed the Northwest Territory to slavery. Southerners, however, saw this as a restraint on slavery, and many of their leaders, most notably John C. Calhoun, resisted any restraint on slavery whatsoever, including territorial restrictions. The Free Soil Party, founded in 1848, opposed the spread of slavery into territories gained from Mexico, a position articulated by David Wilmot in his famous "Proviso." Most Free Soilers were not necessarily abolitionists and actually opposed slavery on the grounds that it was bad for white workers. In any case, this position caused a crisis over the admission of California, whose residents favored a state constitution that banned slavery. The crisis was temporarily resolved with the Compromise of 1850, but Free Soilers emerged again in 1854 when Stephen Douglas introduced the Kansas-Nebraska Act, which opened that territory—contrary to the Missouri Compromise of 1820, to slavery if its residents voted to allow it. Free-Soilers had run as a single-issue party in 1852, but they formed the core of the new Republican Party formed in response to the Kansas-Nebraska Act. The idea was best expressed by Abraham Lincoln, who said that the restriction of slavery where it already existed was a point on which the federal government had to "hold firm, as with a chain of steel." So when Lincoln was elected President in 1860, Southerners felt that slavery was under threat, and they seceded. So, in short, the Free Soil movement, because Southerners saw it as a serious threat, contributed to the outbreak of the Civil War.