The American Revolution had profound effects on the institution of slavery. Several thousand slaves won their freedom by serving on both sides of the War of Independence. As a result of the Revolution, a surprising number of slaves were manumitted, while thousands of others freed themselves by running away.
Nevertheless, slavery received important protections in the Constitution. The notorious three-fifths clause—which counted three-fifths of a state's slave population in apportioning representation—gave the South extra representation in the House of Representatives and extra votes in the Electoral College.
This became the source of tax revenue for local and state governments. Taxes were also levied on slave transactions. Politically, the U.S. Constitution incorporated a feature that made enslaved Africans political capital—to the benefit of southern states.
As the mid-western and northern states continued to grow in economic power and population, slavery became increasingly entangled in every political issue facing the nation, such as nullification, states' rights, and the admission of new territories as states.
The Constitution thus protected slavery by increasing political representation for slave owners and slave states; by limiting, stringently though temporarily, congressional power to regulate the international slave trade; and by protecting the rights of slave owners to recapture their escaped slaves.
The 13th Amendment to the United States Constitution provides that "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."
In addition to the loss of able-bodied workers to the Americas, the slave trade caused wars and slave raids that brought about additional deaths, as well as environmental destruction. Only a few traditional kingdoms (like Benin, a kingdom in southern Nigeria) were able to limit the trade or regulate it with local law.
The estimates based on this new approach suggest that the increase in output per enslaved worker was responsible for roughly a fifth of the growth in commodity output per capita for the United States as a whole between 1839 and 1859—between 18.7 percent and 24.3 percent.
Slavery became more valuable to the Atlantic economy, according to Eltis, because economic growth created a soaring demand for such consumer goods as sugar, coffee, tobacco, and cotton textiles, all of which could be produced cheaply by slaves.
How did slavery affect U.S. political parties in 1860? The Democratic Party split over the issue of slavery. Northern Democrats backed Stephen Douglas and his doctrine of popular sovereignty. Southern Democrats backed Vice-President John Breckinridge of Kentucky.
The slavery issue changed political parties. The Whig Party collapsed, divided between anti slavery Northerners and proslavery Southerners. With this split, a Democrat won the 1852 campaign for president. Some Whigs joined the new American party.
As a result of disagreements over the issue of slavery, splinter parties formed. The Southern Democratic Party spun off from traditional Democrats to nominate John Breckenridge, an advocate of slavery in the West. Republican breakaways formed the Constitutional Union Party.