March 20, 1854: The United States Republican Party is founded.
In early March 1854, the U.S. Senate passed the Kansas-Nebraska Act, which provided for the organization of the eponymous territories and deferred the issue of slavery in both to popular sovereignty. The act effectively overturned the almost sacred Missouri Compromise of 1820, which, for the past three decades, had successfully discouraged conflict between anti- and pro-slavery factions. In reaction to the act, and to the possible expansion of slavery north of the line decreed by the Missouri Compromise, a group primarily composed of ex-members of the nearly defunct Whig Party met in Wisconsin in early 1854. In July of 1854, the Republican Party was officially founded in Jackson, Michigan.
The early Republican Party was united by its rejection of the expansion of slavery, for moral, political, and economic reasons: free-market capitalism and free labor, it was argued, was the superior and more American system. Others feared the disproportionate political power held by slave-owning plantation oligarchs. Naturally, the entirety of party organizational efforts took place in the North. The 1856 Party platform rejected the repeal of the Missouri Compromise and any efforts to expand slavery into free territories; it also supported the construction of a transcontinental railroad and the “improvement of rivers and harbors… for the accommodation and security of our existing commerce”. Its first candidate for the presidency was John C. Frémont, who lost the election to James Buchanan but earned a sizable 38.5% of the popular vote. His campaign slogan, “Free Soil, Free Labor, Free Speech, Free Men, and Frémont”, was lifted from the platform of the Free Soil Party.