The Free Soil Party
The issue of slavery split apart the Democratic Party in the 1840s. In 1848, those who opposed the extension of slavery into the territory acquired from Mexico formed the Free Soil Party. It argued that a system of "free men" working on "free soil" was superior to the slave system. The Free Soil Party pushed for a homestead system, which would make land available to farmers.
Although it was one of the most successful third parties in US history, it did not get its candidates elected, and was absorbed into the Republican Party in 1856.