The only successful secessionist movement in US history

In 1861 about one third of the Union tried to leave the Union. They formed a confederacy of 11 states, pretended that they owned two more than that (Missouri & Kentucky) although they didn't, and then struggled artlessly for four years against the rest of the country in a war that eventually killed 2% of the US population. They failed, of course, because Abraham Lincoln had the power of awesome.

Other people occasionally have tried to tear off pieces of the United States. But America is like the Bébé's Kids of nation states--we don't divide, we kill Indians and take their land. As a history teacher I sometimes have said that the US has never lost territory to another power. But it turns out I'm wrong. There was another secession in 1861, one that was formally aligned with the Confederacy, and this bunch of rebels, unlike their Southron brethren, actually got away with it.

The villain in this assault on American sovereignty was the little village of Town Line, New York. They never got a star on the Confederate flag, but while the boys in blue were stomping Johnny Reb south of the Mason Dixon, Town Line went through the whole war without ever being challenged on their open defiance of the Lincoln Administration. In 1861 they town called a meeting and, acting in bizarre sympathy with the slave states, voted 85 to 40 to leave the USA and join the CSA.

Why would they do that? The reasons are unclear today. The town was along the Underground Railroad, so perhaps some local incident provoked their anger. Talk of secession in the 1860s was not confined to the South, after all. Abolitionists, for entirely different motives, had long criticized the pro-slavery US Constitution and had openly called for leaving the country ever since the Fugitive Slave Act of 1850 was passed. But obviously such sentiments were not those prevailing in Town Line. They voted to side with the slaveholders.

Nor can we dismiss their little unnoticed rebellion as simple opposition to warfare among Americans. Five Townliners (or possibly 12) apparently left their homes, crossed over the battle lines of 1861 and fought on the side of the Confederates. Now, within a year everybody somehow managed to forget about their little rebellion. Perhaps the Rebel volunteers slowly drifted back home--it seems unlikely that many southerners in that parochial age would have been very trusting of a bunch of New York Germans showing up and saying "Ve vant to help you keep your slafes, mein freunden."

As a political unit, Town Line had no chance of exerting any real threat to the rest of New York, upstate New York being a Republican bastion at that time. Had they made any real moves to fight or obstruct the war at home, they'd've been noticed and they'd've been stomped like Tokyo. So everyone just went about their business until the war was over and nobody ever bothered getting around to actually renouncing their one-time defiance of the Union. In fact, nobody even noticed this oddity in the town's record until 1945, when it showed up as a human interest piece in the local paper. World War Two was in progress by then, so Town Line, New York, formally rejoining the United States seemed like the patriotic thing to do. A local referendum reinstated their village's status on January 26th, 1946. But they joined on their own terms (fortunately unconditional) and on their own timeline--after 85 years of unchallenged defiance of the United States government, even if no one knew that's what they were actually doing.