Slavery proved a very inflamed issue in the United States following their victory in the War of 1812, and even more so following their victory in the Mexican-American War, as those both in favor of and in opposition to slavery argued and fought over its existence.
Following the establishment of the Republican Party in 1845, it became even more of a problem. It became clear soon enough that the Northern states, and those in the west - more opposed to the concept of slavery - held majorities in both chambers of Congress. Taking advantage of a division in the Whig Party over the problem, they soon became a force in many areas, and the Whig Party was thrown into extreme disarray. The election of Zachary Taylor in 1848 would be the last gasp for the Whigs - by the end of the decade their membership would largely vanish, moving to the Republicans or Democrats.
While both sides held their own radicals, the moderates remained in the majority. Slowly, they began to move towards a solution, with the precedent established decades earlier for the French population of the state of Quebec making things somewhat more tolerant. The need for this became even more evident when in the elections of 1852, the Republicans won a majority in the House - and their presidential candidate, General Fremont of California, took the presidency in a narrow win over Democrat James Buchanan of Pennsylvania, and John Bell of Tennessee running for the remnant Whigs.
This did not sit well with the South. But, they and their supporters maintained some control, continuing to hold a majority in the Senate.
Events over the next few years would calm down much of the Upper South - but at the same time inflame the so-called "Deep South."
The breaking point, for some, came on May 21st, 1856. Senator Charles Sumner of Massachusetts, one of the more radical Republicans, gave a speech to the Senate, denouncing a bill being proposed by several members of the Senate, which would have allowed slavery in some territories, repealing the compromise of 1820. His rather explicit language infuriated some members from the South, despite the language having many precedents in that body.
The problem was, however, he also spoke of several of the authors of that bill in the process in the same manner. One of these men, Andrew Butler of South Carolina, had a rather hot-headed nephew that was a member of the House.
Viewing it as an extreme insult, this nephew, one Preston Brooks, went after Senator Sumner three days later, on the 24th, as the Senator was doing paperwork. Beating him with a cane, and with fellow Congressman Laurence M. Keitt keeping help away with his pistol, Sumner was badly beaten, with the altercation only ending after the cane in question broke.
Much of the country was stunned at the event - only in the South did Brooks receive any support, and even there, his actions were considered to have gone too far, though have been justified. His home state, of course, was a major exception, as many of the locals considered Sumner's speech to have grievously insulted their state as well.
It came to no surprise for most, then, when both Brooks and Keitt were expelled from the House on June 18th. However, this was not the case in South Carolina. There, it was met with shock, and great anger.