After describing the various way in which slavery is in direct opposition to the principles and practices of democracy, which we've seen in previous posts, Sumner discusses the legal roots of slavery, concluding (p. 19):
Then he discusses the various ways in which slavery retards the general economic progress of the economies of the slave states, or what he calls "the practical results of Slavery." He compares the free states versus the slave states, starting with the argument that the slave states "excel of Free States in all natural advantages," including size, climate and waterways useful for transport. "But Slavery plays tbe part of a Harpy, und defiles the choicest banquet."
And he proceeds to compare the slave and free areas on population growth, total property values (with and without human property counted), agricultural output, manufacturing, domestic and foreign commerce, railroads and canals, postal service ("which is not only the agent of commerce, but of civilization"), charity, education including libraries, press freedom and quantity, patents, literacy among whites, and emigration. He summarizes this portion of his long speech like this:
Thus, at every point is the character of Slavery more and more manifest, rising and dilating into an overshadowing Barbarism, darkening the whole land. Through its influence, population, values of all kinds, manufactures, commerce, railroads, canals, charities, the Post-office, colleges, professional schools, academies, public schools, newspapers, periodicals, books, authorship, inventions, are all stunted, and, under a Government which professes to be founded on the intelligence of the people, one in twelve of the white adults in the region of Slavery is officially reported as unable to read and write. Never was the saying of Montesquieu more triumphantly verified, that countries are not cultivated by reason of their fertility, but by reason of their liberty. To this truth the Slave States constantly testify by every possible voice. Liberty is the powerful agent which drives the plow, the spindle, and the keel; which opens avenues of all kinds; which inspires charity; which awakens a love of knowledge, and supplies the means of gratifying it. Liberty is the first of schoolmasters.The New York Times has the text of the speech online. I rely here on the text from the version published in 1863 as Barbarism of Slavery.