AP PHOTOS: Britain's long, complicated divorce from Europe

Britain's love-hate relationship with the rest of Europe goes back decades, but the Brexit crisis gripping it today stems from a dramatic January 2013 speech by Prime Minister David Cameron in which he promised an "in or out" referendum.

The vote would be to determine whether Britons wanted to stay in the European Union, or sever ties.

The actual referendum was held in June 2016, and Cameron — a youthful prime minister enjoying his second term in office — became its first casualty after he failed to convince voters that the benefits of EU membership outweighed the liabilities.

The vote was 52 percent to 48 in favor of leaving. A chagrined Cameron, with his wife by his side, walked out of 10 Downing Street the morning after and resigned.

Big winners, it seemed, were Boris Johnson and Nigel Farage, luminaries of the "Leave" campaign whose "take back control" arguments carried the day, bolstered by unsubstantiated claims that leaving the EU would allow Britain to add 350 million pounds ($455 million) a week to the National Health Service budget.

But it was Theresa May, Cameron's home secretary, who emerged as the Conservative Party choice as his successor and was charged with the task of leading Britain out of the EU — a task that has turned out to be more difficult than most anticipated.

She formally triggered Britain's departure plan in 2017 by sending the EU a letter invoking Article 50. A March 29, 2019, departure date was set.

So far, so good. But negotiations between Britain and the EU have been slow and at times acrimonious, and the 585-page withdrawal agreement produced after two years of talks has been rejected twice by Britain's divided Parliament.

That has led to Britain's decision to seek a delay in the deadline as May prepares, once again, to seek parliamentary backing. It is not clear what path she will take if she fails a third time.