Stay or go? British voters will decide in June whether to leave the European union, a move that could unravel the E.U.

• Author: Smith, Patricia
• Position: INTERNATIONAL - Essay

On June 23, citizens of the United Kingdom will go to the polls and cast perhaps the most important vote in a generation: They'll decide in a national referendum whether the country should leave the European Union.

"We are approaching one of the biggest decisions this country will face in our lifetimes," says Prime Minister David Cameron, who strongly favors remaining part of the 28-nation bloc. "Leaving Europe would threaten our economic and national security," he adds.

But beyond Cameron, the British government is deeply divided about whether to remain part of the European Union. Six members of Cameron's own cabinet favor a British exit, or "Brexit," and London's outspoken mayor, Boris Johnson, also announced his support for leaving.

"There is only one way to get the change we need," Johnson wrote recently, "and that is to vote to go, because all E.U. history shows that they only really listen to a population when it says no." The European Union is a loose federation of 28 European countries, many of which now share a currency (the euro), free trade, and open borders (see map). A citizen of any E.U. country can live and work legally in any other member nation.

The E.U. came into existence gradually in the decades following the end of World War II. In the war, Germany and Italy were allies against Britain and France. The conflict devastated the continent, and leaders were eager to create an alliance to prevent future wars.

It began as an economic partnership in the 1950s and slowly grew toward a political union. Today, there's a European parliament in Brussels, and a large European bureaucracy regulates many aspects of life across E.U. countries.

From the beginning, the U.K. has been ambivalent toward the European Union. It didn't join until 1973. And in 2002, when 12 European countries gave up their national currencies and began using the euro, Britain said no thanks. It still uses the pound.

The Youth Vote

Those who want to leave argue that Britain can restore control over its borders, trade relationships, and immigration policies only by ducking out of what they see as a dysfunctional, divided, and undemocratic European Union. Former member of Parliament Louise Mensch calls leaving the E.U. "an escape from the ever-greater encroachment of the European superstate on our national sovereignty."

Opinion polls show Britons about evenly divided on whether to stay or leave the union. But young people, who are more idealistic about the E.U.'s...