(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
- 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
- On June 23, the Leave campaign won nearly 52% of the vote in a result that was met with shock around the world and a plunging pound in London.
- The results revealed stark geographical divisions -- London, Scotland and Northern Ireland voted convincingly to Remain, while England and Wales backed Leave.
Cameron resigns
- On June 24, Cameron resigned as Prime Minister, triggering a leadership battle within the Conservative Party.
- Defying initial expectations, former Home Secretary May became the new Prime Minister in July.
A new approach
- 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
- 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?