To understand the meaning of this "missing" 13th Amendment, we must understand its historical context -- the era surrounding the American Revolution. We tend to regard the notion of "Democracy" as benign, harmless, and politically unremarkable. But at the time of the American Revolution, King George III and the other monarchies of Europe saw Democracy as an unnatural, ungodly ideological threat, every bit as dangerously radical as Communism was once regarded by modern Western nations. Just as the 1917 Communist Revolution in Russia spawned other revolutions around the world, the American Revolution provided an example and incentive for people all over the world to overthrow their European monarchies.
Even though the Treaty of Paris ended the Revolutionary War in 1783, the simple fact of our existence threatened the monarchies. The United States stood as a heroic role model for other nations, that inspired them to also struggle against oppressive monarchies. The French Revolution (1789-1799) and the Polish national uprising (1794) were in part encouraged by the American Revolution. Though we stood like a beacon of hope for most of the world, the monarchies regarded the United States as a political typhoid Mary, the principle source of radical democracy that was destroying monarchies around the world. The monarchies must have realized that if the principle source of that infection could be destroyed, the rest of the world might avoid the contagion and the monarchies would be saved.
Their survival at stake, the monarchies sought to destroy or subvert the American system of government. Knowing they couldn't destroy us militarily, they resorted to more covert methods of political subversion, employing spies and secret agents skilled in bribery and legal deception -- it was, perhaps, the first "cold war". Since governments run on money, politicians run for money, and money is the usual enticement to commit treason, much of the monarchy's counter- revolutionary efforts emanated from English banks.