Theresa May's Brexit deal defeated by record margin: What happens now?

In a devastating blow to British Prime Minister Theresa May, the British Parliament rejected a bill Tuesday that lists the terms of the United Kingdom's withdrawal from the European Union — more than two years after the country's historic 2016 referendum that resulted in the decision to depart the E.U.

The House of Commons voted 432 -202 against the deal, said to be the largest defeat in House of Commons history and catastrophic for May.

May had urged Parliament to vote in favor of her Brexit deal, which she struck with the E.U. in November.  But ahead of the vote, signs were not pointing in favor of May, who has faced criticism from members of her own party for her handling of Britain’s departure from the E.U. and in December survived a vote of confidence in the leadership of her party.

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A thumbs-down vote on the divorce deal throws British politics further into turmoil, just 10 weeks before Britain is due to leave the E.U. on March 29. It’s also possible the country could leave the bloc without a deal, which economists have warned could have devastating effects on the British economy.

The deal faced deep opposition from both sides of Britain's divide over Europe. Pro-Brexit lawmakers say the deal will leave Britain bound indefinitely to E.U. rules, while pro-E.U. politicians favor an even closer economic relationship with the bloc.

Here’s what you need to know about Brexit and the departure agreement.

First, what is Brexit?

Brexit — or “British Exit” — refers to the U.K.’s choice to leave the E.U., which is an “economic and political partnership” that currently consists of 28 countries in Europe, according to the BBC.

A list of countries that are part of the E.U. can be found here.

What has happened since the U.K. voted to leave the E.U.?

May and other U.K. leaders have worked with the E.U. to negotiate and agree on the terms of the country’s exit from the E.U., which will occur on March 29 whether or not there is a deal, the BBC reported.

Negotiations between the two sides have led to a 585-page withdrawal agreement. The agreement, in part, details the terms of the U.K.’s departure from the E.U.

Namely, this includes how much money the U.K. is required to pay the E.U., (estimated £39 billion or more than $49 billion), what will happen to the E.U. citizens living in the U.K. and vice versa, and how to prevent a physical border between Northern Ireland and the Republic of Ireland “when it becomes the frontier between the U.K. and the E.U.,” the BBC reported. This has also been referred to as the “backstop plan.”

The E.U. says that there can be no deal without the backstop to guarantee an open border along the U.K.'s only land frontier with an E.U. member state. But pro-Brexit supporters say this part of the agreement will bind the U.K. to many E.U. laws, CNBC reported.

What happens now that Parliament voted “no” on Jan. 15?

Now that Parliament has voted “no” on the deal, May has until Monday of next week to come back to Parliament with Plan B.

The government could try re-submitting the agreement to Parliament after tweaking it or winning some soothing words from the E.U. to assuage lawmakers' concerns.

But while E.U. leaders have offered "clarifications" to the deal, they insist the 585-page withdrawal agreement cannot be reopened.

Other options include possibly delaying Britain's exit or holding a second referendum, which has been driven largely by supporters of the losing "remain" side last time around. But May and her government have firmly opposed this option.

May narrowly survived a no-confidence vote in Parliment on Jan. 16, which was called in the aftermath of the defeat by opposition Labour leader Jeremy Corbyn. The vote was an attempt to trigger a general election.

The House of Commons voted 325-306 in favor of the government.

What’s the so-called “transition period” and why is it important?

The transition period is a period of time between March 29 and Dec. 21, 2020 that will allow businesses to adjust to the new rules between the U.K. and E.U. after Brexit formally begins.

But the transition period will only occur if a deal is met between the E.U. and U.K.

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Economists warn that an abrupt break from the E.U. could batter the British economy and bring chaotic scenes at borders, ports and airports.

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The British government has already reportedly started to plan for this potential outcome.

Fox News' Adam Shaw and The Associated Press contributed to this report.