More than 30 million people from England, Scotland, Wales, Northern Ireland -- and even tiny Gibraltar -- went to the polls, with 51.89% of them deciding that Britain would become the first country to withdraw
from the 28-member bloc.
Yet 48% of voters disagreed with that decision, leaving a remarkably clear picture geographically. London, Scotland and Northern Ireland wanted to remain, while voters in Wales and every English region outside of the capital backed the campaign to leave.
Barely a year after he led his party to a parliamentary majority, many of the traditional Conservative heartlands across the country appeared to turn against their leader following a passionate -- sometimes bitter -- campaign that focused on the economy and immigration
And the repercussions could affect Britain's own union too.
Second Scottish referendum?
Scotland's First Minister Nicola Sturgeon was quick to emphasize that the Scottish people see their future as part of the EU. All 32 of Scotland's local authorities backed the Remain campaign. "Scotland has spoken, and spoken decisively," she said.
Ominous words given that a second referendum on Scotland's own position within the United Kingdom was part of the Scottish National Party's manifesto during the recent Scottish parliamentary election.
Former First Minister and SNP leader Alex Salmond, the architect of the 2014 independence referendum that ended in defeat for the nationalists, warned a second ballot was likely if the country is "dragged" out of the EU.
Meanwhile, Northern Ireland's similar backing for continued EU membership provoked a call by Deputy First Minister Martin McGuinness for a poll on a united Ireland.
He told Irish broadcaster RTE the "Brexit" vote means that "the British government now has no democratic mandate to represent the views of the North in any future negotiations with the European Union and I do believe that there is a democratic imperative for a 'border poll' to be held."
His republican Sinn Fein party have longed back a union with the Republic of Ireland, who are also EU members -- a position that is bitterly opposed by their unionist partners in the government of Northern Ireland who want to preserve their position within the United Kingdom.