A still image taken from footage broadcast by the UK Parliamentary Recording Unit (PRU) on March 29, 2017 shows British Prime Minister Theresa May at the dispatch box making a statement in the House of Commons in London after the letter invoking the provisions of Article 50 of the Lisbon Treaty was delivered to President of the European Council Donald Tusk in Brussels starting Britain's formal withdrawl from the European Union (EU). 
Britain formally launches the process for leaving the European Union on March 29, 2017, a historic step that has divided the country and thrown into question the future of the European unity project. / AFP PHOTO / PRU AND AFP PHOTO / - / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT " AFP PHOTO / PRU " - NO USE FOR ENTERTAINMENT, SATIRICAL, MARKETING OR ADVERTISING CAMPAIGNS-/AFP/Getty Images
Brexit: What happens after Article 50?
01:29 - Source: CNN
CNN  — 

A letter was delivered to Brussels on Wednesday, and not just any letter. This one, signed by UK Prime Minister Theresa May, has triggered Article 50 and officially kicked off the two-year Brexit process.

This is how we got here.

A vote is promised

uk election cameron majority conservative government_00042505.jpg
Cameron to form majority conservative government
04:30 - Source: CNN
  • In 2013, then-UK Prime Minister David Cameron promised a referendum on the UK’s membership of the European Union if his party won the next general election.
  • In May 2015, Cameron’s Conservatives won the election with an outright majority, paving the way for the Brexit vote the following year.

The campaign begins

Boris Johnson addressing supporters during a rally for the 'Vote Leave' campaign
  • The date for the referendum was set as June 23, 2016, and campaigning began. Cameron led the charge for Remain, arguing that “isolationism has never served this country well” and that leaving would be “genuinely a leap in the dark.”
  • There were two separate Leave campaigns, one led by Cameron’s colorful Conservative colleague Boris Johnson – now the Foreign Secretary – and the other by the equally colorful Nigel Farage, then-leader of the Euroskeptic, anti-immigration UK Independence Party. Immigration was the buzzword of both campaigns.

The UK votes to leave

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UK votes to leave the EU in 90 seconds
01:32 - Source: CNN
  • The results revealed stark geographical divisions – London, Scotland and Northern Ireland voted convincingly to Remain, while England and Wales backed Leave.

Cameron resigns

British Prime Minister David Cameron speaks to the press in front of 10 Downing street in central London on June 24, 2016.
Britain has voted to break out of the European Union, striking a thunderous blow against the bloc and spreading panic through world markets Friday as sterling collapsed to a 31-year low. / AFP / ADRIAN DENNIS        (Photo credit should read ADRIAN DENNIS/AFP/Getty Images)
British PM announces resignation
03:02 - Source: CNN

A new approach

Britain's Prime Minister Theresa May delivers a speech on leaving the European Union at Lancaster House in London, Tuesday, Jan. 17, 2017. (AP Photo/Kirsty Wigglesworth, pool)
Theresa May's Brexit speech
01:15 - Source: CNN
  • Despite supporting Remain ahead of the referendum, May has taken a hard line on the UK’s departure from the EU since becoming Prime Minister.
  • Earlier this year, May set out a 12-point plan for the process that included leaving the European Single Market, which allows goods, services and people to move freely through EU states – something many Remainers (and some Leavers) had hoped would not happen.

Article 50

A Union flag flies near the The Elizabeth Tower, commonly known Big Ben, and the Houses of Parliament in London on February 1, 2017.
British MPs are expected Wednesday to approve the first stage of a bill empowering Prime Minister Theresa May to start pulling Britain out of the European Union. Ahead of the vote, which was scheduled to take place at 7:00 pm (1900 GMT), MPs were debating the legislation which would allow the government to trigger Article 50 of the EU's Lisbon Treaty, formally beginning two years of exit negotiations. / AFP / Daniel LEAL-OLIVAS        (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images)
How much will Brexit cost the UK?
01:06 - Source: CNN
  • On Wednesday, May’s letter to European Council President Donald Tusk triggered Article 50, the blueprint that Britain and Brussels must follow to strike a deal on the UK’s withdrawal from the EU.

What happens next?