Britain has voted to remove itself from the European Union in a move that could set off a raft of financial and economic uncertainty across the globe.

An intense campaign over the United Kingdom's place in the continent-wide government came to a head Thursday, with voters deciding they no longer want to work with other nations in the Brussels-based partnership.

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The unprecedented exit of such a major member — referred to as a Brexit — is expected to inject significant uncertainty into financial markets, with some policymakers worrying it could impact the U.S. economy.

Polling leading up to Thursday’s vote indicated an intensely close race, with the side in favor of remaining in the EU seeming to have a slight edge.

The potential for an unprecedented exit of one of the EU’s biggest members has gripped policymakers and financial markets on both sides of the Atlantic.

The campaign to pull out has been driven by growing complaints about Britain’s inability to write and enforce its own laws. The growing number of Middle Eastern refugees seeking solace in Europe has heightened concerns, driving the campaign to pull out of the 28-nation governing body.

The stunning murder of a British politician, Jo Cox, earlier this month cast even further doubt on the high-stakes vote. Cox, a supporter of remaining in the EU, was allegedly killed by a man who called for “freedom for Britain” in court.

In the U.S., some policymakers have openly fretted about what a Brexit could mean for the economy.

Federal Reserve Chairwoman Janet Yellen said that the central bank opted not to raise interest rates earlier this month in part because of the looming Brexit vote and told lawmakers it could carry “significant economic repercussions.”

When he visited the country in April, President Obama warned that if Britain were to leave the EU, it could throw a wrench into efforts to establish a new trade agreement between the two nations.

Obama’s comment that Britain could go to the “back of the queue” for trade talks, while the U.S. continued to hammer out a deal with the remaining EU members, attracted significant attention.

“It could be five years from now, 10 years from now before we were able to actually get something done,” Obama told the BBC. “The U.K. would not be able to negotiate something with the United States faster than the EU.”

Since those remarks, White House officials have emphasized that the president was offering his opinion on the matter, while making clear British voters would have the final say.

But that didn’t stop some Republicans from blasting the president for his remarks, calling it out of bounds for a foreign head of state to weigh in on another country’s domestic affairs.

“I’m going to do exactly what the president did not do and not weigh in on this and send the signal to our great friends and allies in Britain that we stand with them regardless of what decision they make," Ryan said.