The Republic of Texas was a separate nation from 1836-46 before joining the United States. And now, in 2012, more than 115,000 Texans have signed a petition calling for the Lone Star State to secede from the U.S. so that it can again be on its own.

Though Texas is leading the 21st century breaking-away way, more than 25,000 South Carolinians have recently signed a secession petition for our state to bolt, too.

It was the other way around on Dec. 20, 1860, when South Carolina became the first state to secede from the U.S. Ten other states — Texas among them — followed over the next six months to form the Confederate States of America.

Their attempt to leave the Union sparked a transforming war with a death toll of more than 600,000 before the seceded states were brought back into the U.S. by force of arms.

According to a constitutional scholar sitting on our nation’s highest court in this 21st century, that outcome ended any debate about whether a state could choose to leave the United States.

As he wrote in 2006: “If there was any constitutional issue resolved by the Civil War, it is that there is no right to secede.”

That expert legal opinion wasn’t delivered by a liberal. It was delivered by conservative Supreme Court Justice Antonin Scalia.

But some Americans are again foolishly advocating that their states secede. Most of the modern-day secessionists seem particularly distressed by the re-election of President Barack Obama.

All of them should know better than to imagine that secession is a rational response to this electoral result.

Yes, the Founding Fathers were themselves secessionists. On July 4, 1776, they acted on their proclaimed right “to dissolve the political bands” tying them to Great Britain.

Yes, secession sentiment was strong in New England during the War of 1812, which was quite unpopular in that region. Delegates from those states met in Hartford, Conn., in 1814 to decide whether or not to secede before prudently rejecting that option.

Yet their mere consideration of the question showed that even some Northern folks of that time assumed a right to secede.

And South Carolina threatened secession over the tariff nullification crisis in 1833 before backing down from President Andrew Jackson — the only president born in our state.

However, the U.S. Supreme Court’s 1868 decision in Texas vs. White ruled that the states lack secession power.

Texas Gov. Rick Perry, during an April 2009 Tea Party rally, asserted that his state alone had that right. Numerous historians then pointed out that while such a prerogative was discussed during the negotiations that brought Texas into the U.S. in 1846, it was not part of the final deal.

Still, that hasn’t lowered the current secession fever.

But why? The idea of any state again trying to leave our Union is preposterous.

Texas Congressman Ron Paul, who has run for president once as a Libertarian (1988) and twice as a Republican (2008 and 2012), wrote on his House website this week that secession is a “deeply American principle.”

Rep. Paul added: “If people or states are not free to leave the United States as a last resort, can they really think of themselves as free? If a people cannot secede from an oppressive government, they cannot truly be considered free.”

Keep in mind that the perceived freedom to secede was exercised by this and most other Confederate states, in large part, to assure the continuation of slavery.

So here’s a truly “deep American principle” to remember:

Seceding from the United States isn’t just stupid. It can be, as it was a century and a half ago, disastrous.

And that’s a lasting lesson our state learned the hard way.