In 1860, in perhaps the greatest turning point of the career of the sixteenth president of the United States, Lincoln gave a speech that transcended his figure from a joking yokel to a serious national force.

Lincoln Outlines his Ideas on SlaveryLincoln had been invited east to speak at a series of lectures held by Plymouth Church, where word had spread about his able debates with Illinois Senator Stephen M. Douglas. Much of the debates had been over the issue of slavery, particularly its expansion into the new territories gained from the Mexican-American War. Popular sovereignty had created Bleeding Kansas, where Free-Staters and Bloody Ruffians had killed dozens of people in the fight over whether the territory would become a free or slave state. It was obvious that this strategy could not continue, and the actions of vigilante John Brown had shown that abolitionists meant to end slavery completely, some by any means necessary.

When Lincoln accepted the invitation, he began to pore over legal and political precedence to determine what exactly the spirit of America thought of slavery. He worked for months, causing William Herndon, his law partner, to note, "No former effort in the line of speech-making had cost Lincoln so much time and thought as this one". After diligently outlining the careers and beliefs of each of the thirty-nine Founding Fathers of America, he traced twenty-one of them to speaking for limitation on slavery, particularly the matter of controlling its spread to new territories, first the Northwest Territory in the Ohio Valley, then the Louisiana Purchase. Rather than stop at this, however, he decided to show the future of what could be done by beginning the end of slavery in all states.

A new story by Jeff ProvineLincoln gave an enormous 7,000 word speech (one of the longest of his career), tackling nearly all of the angles on the issue of slavery. He commented on the flip-flopping of politicians such as his old rival Stephen Douglas and Chief Justice Roger Taney. He also rebuked those who suspected Republicans of being willing to resort to violence to end slavery and showed that they "have failed to implicate a single Republican in his Harper's Ferry enterprise" and that "John Brown was no Republican". Instead, the Republicans would do their work through the polls, legally and without force. To those who refused to acknowledge Federal authority and called for secession, he said, "But you will not abide the election of a Republican president! In that supposed event, you say, you will destroy the Union; and then, you say, the great crime of having destroyed it will be upon us! That is cool. A highwayman holds a pistol to my ear, and mutters through his teeth, "Stand and deliver, or I shall kill you, and then you will be a murderer!", a point that would be upheld by the Constitutional Unionists later in the election that November.

Later in the speech (which ended with a rallying cry to the Republican Party about their "sense of duty" and "right makes might"), he answered the question of what to do with freed slaves in a society where "a physical difference between the white and the black races which will forever forbid the two races living together on social or political equality" (a quote from his own 1858 speech in Charleston, IL) that rather segregation was the answer and that the Republicans ought to support efforts to "..colonize persons of African descent, with their consent, upon this continent or elsewhere, with the previously obtained consent of the government existing there". Perhaps most critically, he explained that ending slavery could also be a boon for the nation as freedmen could purchase freedom with government bonds, which would be repaid in full over a few years' taxes for the new citizen.

The speech was greeted by much applause, and one audience member described Lincoln with, "his face lighted up as with an inward fire; the whole man was transfigured. I forgot his clothes, his personal appearance, and his individual peculiarities.". Cooper Union proved to New Yorkers and Easterners overall that Lincoln would make a great campaign. At the 1860 Republican National Convention, Lincoln took the lead as other candidates had fallen back: William Seward the radical had bungled his attempts to moderate, Whigs distrusted Salmon Chase over tariffs, and Edward Bates was opposed by immigrants. Lincoln handily won the ticket, and, in November, won the election as the Democratic party was in pieces.

Many Southerners called to secede, but their voices were drowned out by many slaveholders who stood to make a great deal of money "liberating" their slaves with the government paying market rates to cover "loss of property" in voluntary compensated emancipation. While the Emancipation Act of 1862 was to be followed only at will, a wave of slaves hurried to gain their freedom. The question of what to do with so many freedmen (few embraced the idea of going back to Africa, despite the pamphlets of the American Colonization Society) was solved with the Homestead Act of 1862, populating much of the territories with free land proved up by former slaves. Lincoln's two terms further expanded federalism by promoting large works projects such as the Intercontinental Railway (completed in 1865), followed by an abandoned effort at digging a Panama Canal suggested by Representative Benjamin Butler.

War with Spain broke out in 1870 after the execution of Captain Joseph Fry and 52 others as pirates, leading to American capture of much of Spain's Caribbean holdings by 1872. It was an expansionistic dream long held by many Southerners, proud to see the Stars and Stripes above new capitals.