Freesoilers, the name of a political party in the United States, founded upon the principle of non-extension of slavery to the territories. It was an outgrowth of the liberty party in 1840, and was merged in the republican party in 1856. The immediate cause of its establishment was the acquisition of new territory at the conclusion of the Mexican war. In 1840, to a bill in congress making an appropriation to negotiate a peace with Mexico, David Wilmot, a democratic representative from Pennsylvania, offered an amendment, known as the Wilmot proviso, that there shall be neither slavery nor involuntary servitude in any territory on the continent of America, which shall hereafter be acquired by or annexed to the United States by virtue of this appropriation, or in any other manner whatsoever, except for crime," etc. It was carried in the house, but failed in the senate, and in the next session was defeated in both branches. Peace with Mexico, however, and the consequent acquisition of territory, made the Wilmot proviso of political and practical importance. In both the whig and democratic national conventions in 1846 there were delegates from the northern states who attempted to introduce into the party platforms of that year resolutions prohibiting the extension of slavery to the territories.

The rejection of these resolutions led to the secession of a considerable number of prominent men from both parties, especially in Massachusetts, New York, and Ohio. In New York seceding democrats were termed barnburners," and their secession was partly on personal as well as on anti-slavery grounds. The seceders from both parties united, and sent delegates from all the free states, and from Delaware, Maryland, Virginia, and the District of Columbia, who met in convention at Buffalo, N. Y., x\ug. 9, 1848, and formed a freesoil party. They nominated for president and vice president of the United States Martin Van Buren and Charles Francis Adams. In November following this ticket received a popular vote of 291,000, but did not secure a single electoral vote. The second national convention of the freesoil party, at Pittsburgh, Pa., Aug. 11, 1852, comprised delegates from all the free states, and from Delaware, Maryland, Virginia, and Kentucky, and nominated for president and vice president of the United States John P. Hale and George W. Julian, who in the election following received a popular vote of 157,000. The so-called compromise measures of 1850 and the repeal of the Missouri compromise in 1854, by the Kansas-Nebraska act, with the political agitation following, for a time gave great prominence to the platform and principles of the freesoil party.

It formed the nucleus of the republican party, which was founded in 1850 chiefly from the dissolving whig party. The adoption by the republicans of the freesoil platform in respect to slavery ended the freesoilers as a distinctive party.