Frank Langfitt

Updated at 6:54 p.m. ET

More than 3 1/2 years after the landmark Brexit referendum, the United Kingdom finally left the European Union at 11 p.m. GMT on Friday.

That means Britain exited the bloc of 27 remaining countries and will begin to forge its own way in the world, but there's a transition period before the U.K. cuts itself off entirely.

The U.K. has been a member of the EU since 1973. Leaving is one of the biggest, riskiest and most divisive steps the country has taken in decades.

Voters in the United Kingdom head to the polls Thursday for a crucial election that could determine the country's future, and how and when it will break off from the European Union.

This will be the fifth major vote in the country in less than five years — including two previous general elections, European Parliament elections and the Brexit referendum — a sign of how chaotic British politics have become.

The stakes are high, voters are weary and the two main candidates for prime minister are especially polarizing.

The European Union and the United Kingdom reached a new Brexit agreement on Thursday, and while it appeared to mark a big breakthrough in the years-long process, the saga doesn't end here.

The withdrawal deal still needs approval in both the U.K. and European parliaments. Although EU leaders unanimously endorsed it in Brussels on Thursday, it faces stiff opposition in Britain's Parliament, which has voted down three previous Brexit deals.

The U.K. is scheduled to leave the EU on Oct. 31.

Updated at 6 p.m. ET

British Prime Minister Boris Johnson says he is ready to call a snap election after lawmakers cleared the way for a vote on Wednesday to prevent the U.K. from leaving the European Union without a withdrawal agreement at the end of October.

The announcement was the culmination of a dramatic day that saw a defection rob Johnson and his ruling Conservative Party of their single-seat majority in Parliament.

Even by the standards of the Brexit era, this has been an extraordinarily turbulent week for the United Kingdom.

Queen Elizabeth II agreed to grant Prime Minister Boris Johnson's request to suspend Parliament, just as legislators are rising to block his threat to crash the country out of the European Union.

The United Kingdom is headed for another showdown next month over Brexit, an issue that has paralyzed British politics for several years and ended the careers of the two previous prime ministers.

This year, Parliament thrice defeated a U.K. withdrawal agreement that then-Prime Minister Theresa May's government had negotiated with the European Union. Parliament reconvenes on Sept. 3.

Here are some of the key challenges facing Boris Johnson, the new prime minister, who has vowed to take the U.K. out of the European Union one way or another on Oct. 31.

Britain would face gridlock at ports; shortages of medicine, fuel and food; and a hard border with Ireland if it left the European Union with no deal, according to a leaked government document.

At a time of polarization and political chaos, the United Kingdom and the United States are about to be led by two remarkably similar figures. On Tuesday, Britain's ruling Conservative Party elected Boris Johnson as their leader by an overwhelming margin, sending him to No. 10 Downing Street. He will take office on Wednesday.

When the Mail on Sunday published private assessments of the White House from the British ambassador to the United States, President Trump expressed outrage.

In a leaked cable, Ambassador Kim Darroch called the White House "inept" and "incompetent" and said the president "radiates insecurity." Trump called Darroch "stupid" and said he wouldn't deal with him.

Boris Johnson is a larger-than-life British politician who likes to project the image of a bumbling, fun-loving man of the people.

His many supporters in Britain's Conservative Party find him charismatic, entertaining and — to their minds — refreshingly politically incorrect.

Many critics, however, see him as unprincipled, offensive and driven wholly by ambition.

The special relationship between the United States and the United Kingdom may not feel very special at the moment. President Trump's three-day visit to the U.K. got off to a rocky start on Monday, when he launched a Twitter attack on London Mayor Sadiq Khan as Air Force One was preparing to land.

British voters are expected to deliver a humiliating defeat to Prime Minister Theresa May's Conservative Party in European Parliament elections on Thursday. Many who want Britain to pull out of the European Union are angry with May, who is under heavy pressure to resign, for failing to deliver on the Brexit referendum result nearly three years ago.

When the United Kingdom voted for Brexit nearly three years ago, some thought it might mark the beginning of the end of the European Union. Some analysts warned the U.K. would be the first in a series of dominoes to fall and spoke of a possible "Frexit," "Nexit" and "Swexit."

Protesters demanding government action on climate change disrupted traffic and public transit around London on Wednesday, the third day of climate demonstrations in the capital.

"Are you angry?" yelled Will Grover, a councillor with Prime Minister Theresa May's Conservative Party.

"Yes!" yelled back the mostly older crowd.

"You should be," said Grover, "because your voice, your vote, is being betrayed. They do not respect you. Why should you respect them?"

Brexit has convulsed the United Kingdom like no other political event in decades, but it can be hard to follow the day-to-day machinations. At the end of a chaotic week, here's what to know.

How different are things now for the U.K. than they were on Monday?

Updated Thursday at 9:38 a.m. ET

This week marks a turning point for Britain and Brexit. On Tuesday, the British Parliament voted down Prime Minister Theresa May's Brexit plan for the second time. On Wednesday, lawmakers voted against a "no-deal Brexit" — leaving the European Union without a formal agreement with Brussels.

Today, they will vote on whether to postpone Brexit beyond the scheduled departure date of March 29.

Here's what you need to know.

What happened on Tuesday?

The Packhorse pub sits in the tiny village of South Stoke in the west of England amid rolling hills dotted with sheep. For more than a century and a half, it played a crucial role in the village and marked milestones in the lives of local families.

Gerard Coles, who was born half a mile from the pub and now brews cider nearby, started coming to the Packhorse when he was 15 and underage, sometimes with his school teacher for lunch.

Valentine's Day is usually a boon for florists. But in the United Kingdom, a cloud hangs over the industry.

Rosa Ashby, who runs Rosa Flowers in the English market town of Witney, is anxious. Every flower in her shop, including lilies, chrysanthemums and lisianthus, is either grown in or distributed through the Netherlands. That has worked just fine since Ashby started her business 22 years ago, because the U.K. has been inside the European Union's single market, and flowers — and countless other products — have flowed seamlessly across the border.

In the rush of digital news that washes over so many of us every day, it's hard to remember what a politician might have said or promised several weeks ago, let alone several years. Some activists in the United Kingdom have come up with an imaginative, seemingly old-fashioned solution to this modern-day problem.

They plan to put up at least 150 billboards across the U.K. quoting some of the promises and rosy predictions politicians made about Brexit in recent years so people can reconsider them amid the political chaos that has followed.

British Prime Minister Theresa May's Brexit plan went down to an historic defeat in Parliament on Tuesday. The next day, she narrowly survived a vote of no-confidence in her government. This Monday, Jan. 21, she'll have to tell Parliament what her Plan B for Brexit is — and will submit that plan to a vote on Jan. 29.

Here's what to know about key issues during this extraordinary and chaotic moment in British politics.

After Tuesday's staggering loss, most politicians would have resigned. Why is Theresa May still in office?

Norway's rugged west coast is home to glaciers, waterfalls and dozens of fjords that draw hordes of tourists each summer. But navigating the extreme topography of the region, which is home to a third of the country's population, isn't easy.

Not so long ago, staging another Brexit referendum in the United Kingdom seemed almost unthinkable. But in recent weeks, as calls have grown louder, the unthinkable has begun to seem plausible.

Last week, former Prime Minister Tony Blair said because of the current political chaos and future economic risks, the British should have another say on whether to leave the European Union if there are no other viable options.

The United Kingdom is embroiled in its biggest political crisis in decades. On Wednesday evening, members of Parliament in Prime Minister Theresa May's own Conservative Party are casting ballots in a no-confidence vote over her leadership. May needs to win a simple majority of votes from her party's parliamentarians to keep her job.

Here's what you need to know.

Why do members of the prime minister's own party want to sack her?

On Thursday officials from the United Kingdom and the European Union approved a draft agreement on their future relationship for when the U.K. leaves at the end of March 2019. The deal, which is not legally binding, calls for an "ambitious, broad, deep and flexible partnership," including a trading relationship on goods that is "as close as possible."

This week was one of the most chaotic in British politics in recent decades. After more than a year of negotiations, Prime Minister Theresa May presented a Brexit withdrawal agreement from the European Union that seemed to unite British politicians across the spectrum in their hatred for it.