The modern day Republican party is descended from anti-slavery leaders from the Whig, Free-Soil and Democratic parties. They formed the Republican Party in response to the Kansas-Nebraska Act of 1856, which allowed settlers to determine whether or not a state would establish slavery.
The first semblance of the Republican Party started with the Missouri Compromise of 1820, which allowed the expansion of slavery into western lands. The Missouri Compromise was replaced by the Kansas-Nebraska Act, which further ostracized opponents of slavery. Pioneers of the Republican Party wanted to eliminate expansion of slavery into new territories and abolish the slave system altogether.
Leaders conducted two separate meetings in 1854 that eventually gave birth to the Republican Party. Republicans gave the nomination to John C. Fremont in 1856, whose main platform was the urging of Congress to end slavery. He lost the presidency, but his party replaced the Whigs as the primary opposition to the Democratic Party.
The Republican Party retained some of its Free-Soil roots by championing the grant of western lands to farmers instead of allowing slave owners to purchase the best land available. The party also advocated modernizing America through the expansion of banking, factories and railroads. They promoted the idea of free-market labor as a beneficial alternative to slavery. Churches played a prominent role in the party by promoting the restriction of sins in the form of slavery, alcohol and polygamy. Republican Abraham Lincoln won the presidency, but the country descended into civil war over slavery shortly thereafter.