Meanwhile a subject of far greater interest called out the best energies of Mr. Clay,—­the beginning of a memorable struggle, even the agitation of the Slavery question, which was not to end until all the slaves in the United States were emancipated by a single stroke of Abraham Lincoln’s pen.  So long as the products of slave labor were unprofitable, through the exhaustion of the tobacco-fields, there was a sort of sentimental philanthropy among disinterested Southern men tending to a partial emancipation; but when the cotton gin (invented in 1793) had trebled the value of slaves, and the breeding of them became a profitable industry, the philanthropy of the planters vanished.  The English demand for American cotton grew rapidly, and in 1813 Francis C. Lowell established cotton manufactures in New England, so that cotton leaped into great importance.  Thus the South had now become jealous of interference with its “favorite institution.”

In an address in Manchester, England, October, 1863,—­the first of that tremendous series of mob-controlling speeches with which Henry Ward Beecher put a check on the English government by convincing the English people of the righteousness of the Federal cause during our Civil War,—­that “minister-plenipotentiary,” as Oliver Wendell Holmes called him, gave a witty summary of this change.  After showing that the great Fathers of Revolutionary times, and notably the great Southerners, were antislavery men; that the first abolition society was formed in the Middle and Border States, and not in the Northeast; and that emancipation was enacted by the Eastern and Middle States as a natural consequence of the growth of that sentiment, the orator said:—­

“What was it, then, when the country had advanced so far towards universal emancipation in the period of our national formation, that stopped this onward tide?  First, the wonderful demand for cotton throughout the world, precisely when, from the invention of the cotton gin, it became easy to turn it to service.  Slaves that before had been worth from three to four hundred dollars began to be worth six hundred dollars.  That knocked away one third of adherence to the moral law.  Then they became worth seven hundred dollars, and half the law went; then, eight or nine hundred dollars, and there was no such thing as moral law; then, one thousand or twelve hundred dollars,—­and slavery became one of the Beatitudes.”

Therefore, when in 1818 the territory of Missouri applied for admission to the Union as a State, the South was greatly excited by the proposition from Mr. Tallmadge, of New York, that its admission should be conditioned upon the prohibition of slavery within its limits.  It was a revelation to the people of the North that so bitter a feeling should be aroused by opposition to the extension of an acknowledged evil, which had been abolished in all their own States.  The Southern leaders, on their side, maintained that Congress could not, under the Constitution, legislate