The American idea, Parker declared in an 1850 speech, comprised three elements: that all people are created equal, that all possess unalienable rights, and that all should have the opportunity to develop and enjoy those rights. Securing them required “a government of all the people, by all the people, for all the people,” Parker said.
But even in Boston, democracy was embattled. The state’s government was in the grip of the nativist Know-Nothings, who resented recent waves of immigrants. That same Friday, voters had ratified an amendment imposing a literacy test for voting, a mostly symbolic effort at exclusion. [...]

The fight against slavery had become a struggle for the American idea; the two could not coexist. In 1860, Abraham Lincoln’s election led the South to conclude that it had lost the argument. The seceding states left Congress with a Republican majority, able to translate the principles of equality, rights, and opportunity into practical action: homesteads for all who sought them; land-grant colleges to spread the fruits of education; tariffs to protect fledgling industries; and a transcontinental railroad to promote commerce and communication. Here was the American idea made manifest.