The US went on to champion secession from its early days and even to military back multiple secession movements around the world be it Panama from Colombia, Bosnia from Yugoslavia, Kosovo from Serbia, etc. This was a typical view:
"Any people anywhere being inclined and having the power, have the right to rise up and shake off the existing government, and form a new one that suits them better. This is a most valuable, a most sacred right - a right which we hope and believe is to liberate the world. Nor is this right confined to cases in which the whole people of an existing government may choose to exercise it. Any portion of such people, that can, may revolutionize, and make their own of so much of the territory as they inhabit.” Abraham Lincoln January 12, 1848
Yet when some of its own sovereign states no longer consented to be ruled over by it, imperial Washington could not stand it and immediately got violent. Outside the US, everybody else very much noticed the blatant hypocrisy.
Times of London hit the nail on the head in September 1862:
“If the Northerners on ascertaining the resolution of the South, had peaceably allowed the seceders to depart, the result might fairly have been quoted as illustrating the advantages of Democracy; but when Republicans put empire above liberty, and resorted to political oppression and war rather than suffer any abatement of national power, it was clear that nature at Washington was precisely the same as nature at St. Petersburg. There was not, in fact, a single argument advanced in defense of the war against the South which might not have been advanced with exactly the same force for the subjugation of Hungary or Poland. Democracy broke down, not when the Union ceased to be agreeable to all its constituent States, but when it was upheld, like any other Empire, by force of arms.”
Abraham Lincoln January 12, 1848
"When you strike at a king, you must kill him."
― Ralph Waldo Emerson
Exactly. It’s the one argument for which the southernphobes have no rebuttal. Well, no legitimate rebuttal.
It’s an argument based on logic, not emotion. And not “free the slaves,” which Lincoln argued was not the reason for the war.