It would be incredibly difficult for California to pull off a 'Calexit' and secede from the US

Lucy Nicholson/Reuters

Protesters hold up signs during a march and rally against the election of President Donald Trump in Los Angeles, California.

The last time a state seceded from the US, it was the 1860s and a civil war broke out.

Still, history hasn't stopped a small group of Californians from pursuing a breakaway from the union in the wake of President Donald Trump's rise to office.

Since the election, the "Calexit" movement has grown from a hashtag trending on social media to a legitimate campaign for California's independence. Secession backers are now collecting voter signatures to get a measure on the 2019 state ballot which, if passed, would help clear a path for legal secession.

One in three Californians surveyed by Reuters/Ipsos in a recent poll want the state to leave the US. Still, the event of a Brexit-like secession remains unlikely.

Many opponents have taken to Twitter to remind Calexit backers that Texas already tried to secede in the past - and failed miserably.

Texas has attempted a "Texit" time and time again. Residents of the Lone Star State passed resolutions calling for a vote on secession recent as March 2016.

One big obstacle: The US Constitution lays out procedures for how a new state may enter the union, but there are no protocols for a nation to exit.

"There's no legal path to secession," Cynthia Nicoletti, an associate professor of law at University of Virginia School of Law and author of the upcoming book, "The Treason Trial of Jefferson Davis: Secession in the Aftermath of the Civil War," told Business Insider last year.

Shortly after Barack Obama was re-elected to the presidency in 2012, disgruntled Texans filed a petition to the White House asking that the administration "peacefully grant" the state the right to withdraw from the union. It racked up over 125,000 signatures. The director of the White House Office of Public Engagement, Jon Carson, dashed their dreams in his response.

Carson wrote that our founding fathers established in the US Constitution "the right to change our national government ... But they did not provide a right to walk away from it."

Brian Bahr/Getty

The Texas Longhorns mascot leads the team onto the field before a football game.

That leaves two paths, according to Nicoletti. "You're going to need a constitutional amendment or you're going to need a revolution," she said.

In 1861, Texas rallied with 10 other southern states to leave the union and form the Confederate States of America. It didn't turn out as they hoped, needless to say. About 700,000 people died in the Civil War, and by 1870, all 11 states rejoined the US.

According to a significant case argued before the US Supreme Court in 1869, they never had the right to exit in the first place.

Nicoletti, a legal historian who said she was surprised to find her subject of expertise relevant once again, explains that while the issue of a state's legal right to secede may have played out on the battlefield when the North defeated the South, Texas v. White made it crystal clear that individual states could not just leave - even if agreed upon by a majority of Texans.

Still, "saying that something is illegal is not the same as saying it's impossible," Nicoletti said.

A state can pass a constitutional amendment that legalizes secession with a vote from three-fourths of the other 49 states. However, Fusion pointed out that amending the Constitution "is a feat difficult enough that it has happened only 17 times in 227 years."

Rich Pedroncelli/AP

Marcus Ruiz Evans, of The Yes California Independence Campaign, talks to passersby about California succeeding from the US and becoming its own nation.

The Yes California Independence Campaign, the political action committee leading the Calexit charge, is currently gathering signatures to put a measure on the ballot in 2019 that would allow Californians to voice their support for a departure from the US. If at least half of registered voters show up at the polls for that vote, and at least 55% vote in favor of secession, the results would serve as the state's declaration of independence, the LA Times reports.

If it passes, which is highly implausible, the group may do a few things.

A member of the California federal delegation could go to Washington, DC, and propose an amendment to the US Constitution that would permit the state to bounce the union.

Alternatively, California could call for a convention of the states and the amendment granting California its independence could be voted upon by the delegates to the convention.

Either option ends with a call for congressional approval. Nicoletti said the chances Calexit succeeds are slim to none, and the potential consequences are grim.

"The last time [a state seceded], the consequence was the Union Army," Nicolleti said. "Do I think that there will be troops in the center of San Francisco? I don't know, I mean, I don't know that I take this idea of secession all that seriously."