William Jennings Bryan delivered this incredible speech at the Democratic National Convention in Chicago (1896). The quoted portion is the very last line of the speech, and purportedly caused the crowd to go absolutely wild.

The speech, of course, was about the gold standard (or more accurately, the dilution of the gold standard). From the inception of the USA until relatively recently, the US adhered to a gold standard—that is, our currency (the dollar) was backed by gold. There are advantages and disadvantages to having a metallic standard (or any standard, for that matter), but, given that this is US History and not Economics, that discussion is beyond the scope of this question. 

The “Crime of ‘73” refers to the Coinage Act of 1873. The Coinage Act of 1873 was (or at least, came to be) an extraordinarily controversial law (hence the moniker “Crime of ‘73”). Essentially, the law ended the free coinage of silver, and placed the US firmly on the gold standard. This, like most laws, infuriated some people while it greatly pleased others.

Those advocating deflation were happiest with the bill, because the gold standard is a deflationary measure for currency; those advocating inflation were incredibly displeased with the bill, because the gold standard is a deflationary measure.

Those agitating for inflation wanted the free coinage of silver, because injecting silver into the monetary supply created inflation (along with more currency in circulation).

The “Stalwarts” led by Senator Conkling heavily favored the spoils system, and thus opposed civil-service reform. Remember: the spoils system was a political incarnation of “to the victor goes the spoils”; in other words, the party member who won the election was supposed to fill the vacant bureaucracy seats with his friends and supporters who helped him get elected. Obviously, the Stalwarts weren’t too fond of civil service reform—which sought to do away with, or at least decrease, the spoils. 

The “Half-Breeds” were a faction of the Republican Party that were in direct opposition to the Stalwarts, but still voted Republican. The Half-Breeds were led by Senator James G. Blaine. The name “half-breed” was supposedly signified the Stalwarts’ contempt of the Half-Breeds—that the Stalwarts viewed the Half-Breeds as only half-Republican.

Interestingly, the Mugwumps were a faction of the Republican Party that voted Democrat (just for Cleveland). The reason being that the Mugwumps were firm believers in civil-service reform, and just didn’t quite think that Blane, the Half-Breed candidate, was up to the challenge.

In reaction to Abraham Lincoln's election as president, South Carolina was the first state to secede, doing so in December 1860. Georgia and Mississippi seceded in January 1861. Virginia and North Carolina did not secede until after the Battle of Fort Sumter in April 1861.

As a result of the Missouri Compromise, Maine entered the Union as a free state, but is not listed as any of the choices. Missouri entered the Union as a slave state. California, Kansas, and Nebraska were not a part of the compromise, and they all entered the Union as free states decades after the compromise.

California entered the Union as a free state as one of the provisions of the compromise. Missouri had already gained statehood as a slave state decades earlier. Nebraska and Kansas were not part of the compromise, gaining statehood years later.

Although most slave states seceded from the Union in 1860-1861 to form the Confederate States, a few Border States where slavery was legal remained loyal to the United States. The loyal Border States included Missouri, Kentucky, Maryland, and Delaware. During the war, the pro-Union areas of western Virginia seceded from Virginia to form the new state of West Virginia. Although the Border States officially remained loyal to the United States, citizens from every Border State fought on both sides of the American Civil War.

Slavery was not completely abolished in the United States until the ratification of the Thirteenth Amendment in 1865. The other answers restricted slavery to some extent, but did not completely abolish it. The 1887 Northwest Ordinance prohibited slavery in territories north of the Ohio River that were annexed by the United States from Great Britain after the Revolutionary War. The 1820 Missouri Compromise prohibited slavery in the land purchased by the United States from France in 1803, except for the state of Missouri. The Civil War-era Confiscation Acts allowed the Union army to confiscate and free slaves whose masters had rebelled against the United States. The Emancipation Proclamation was put forth by President Lincoln in 1862. Lincoln used his war powers to free every slave in the Confederacy if those states did not return to the Union by January 1, 1863. However, the Proclamation did not free any slaves in loyal Border States like Kentucky, or in territories of the Confederacy that had already been conquered by the Union Army in 1862.