The Library of Congress offers this collection of primary source documents related to South Carolina and the Nullification Crisis that occurred during the presidency of Andrew Jackson.
The American Treasures collection of the Library of Congress includes this exhibit of the Compromise of 1850. Check out the original manuscript with corrections written by South Carolina Senator John C. Calhoun. The site also features helpful notes about the resolutions in the Compromise and the debates they sparked.
The National Park Service of the U.S. Department of the Interior has compiled the transcripts of the Lincoln-Douglas debates, a series of political key debates between Abraham Lincoln and Stephen A. Douglas during the 1858 campaign for the Illinois Senate seat.
The Cornell University Library offers digital access to its extensive Making of American Journal Collection. Search by key word or simply browse the pages of several nineteenth-century magazines, many of which circulated during the years leading up to the Civil War.
The University of Virginia presents the transcripts of several eyewitness accounts of radical abolitionist John Brown's raid, his capture, and his trial.
Washington State University offers a rich collection of primary source documents related to the life and work of Harriet Beecher Stowe, the author of Uncle Tom's Cabin (1852), an incendiary work of abolitionist fiction reviled by southerners.
Washington University in St. Louis has put together an extremely user-friendly website dedicated to the Dred Scott case, featuring a full historical timeline and complete court documentation.