LONDON — Britain’s startling decision to pull out of the European Union set off a cascade of aftershocks on Friday, costing Prime Minister David Cameron his job, plunging the financial markets into turmoil, and leaving the country’s future in doubt.

The decisive win by the “Leave’’ campaign exposed deep divides: young versus old, urban versus rural, Scotland versus England. The recriminations flew fast, not least at Cameron, who had made the decision to call the referendum on membership in the bloc to manage a rebellion in his own Conservative Party, only to have it destroy his government and tarnish his legacy.

The result of the so-called Brexit vote presented another stiff challenge to the leaders of the other major European powers as they confront spreading populist anger. It was seized on by far-right and anti-Brussels parties across Europe, with Marine Le Pen of the National Front in France calling for a “Frexit’’ referendum and Geert Wilders of the Party for Freedom in the Netherlands calling for a “Nexit.’’

European officials met in Brussels to begin discussing a response and to emphasize their commitment to strengthening and improving the bloc, which will have 27 members after Britain’s departure.

“At stake is the breakup, pure and simple, of the union,’’ Prime Minister Manuel Valls of France said, adding, “Now is the time to invent another Europe.’’

Germany urged calm. “Today marks a turning point for Europe,’’ Chancellor Angela Merkel said. “It is a turning point for the European unification process.’’

Financial markets swooned as it became apparent that the Leave forces would prevail, with the British pound and global stock prices plummeting in value early Friday as the vote tally showed the Remain camp falling further behind.

President Obama on Friday sought to assure Britain and the European Union that the United States would not pick sides once the two are divorced. Rather than dwell on the wrenching change to come, Obama emphasized continuity. “One thing that will not change is the special relationship that exists between our two nations,’’ he said. “That will endure.’’ And, he added, “The EU will remain one of our indispensable partners.’’

The president said he had spoken with Cameron, who told him Britain’s departure would be orderly, and with Merkel, who will loom even larger as a partner for the United States in a European club that no longer has a Britain as a member.

With all votes counted, Leave was ahead by 52 percent to 48 percent, an enormous snub to Britain’s elite.

The process of withdrawal is likely to play out slowly, perhaps taking years. It will mean pulling out of the world’s largest trading zone, with 508 million residents, including the 65 million people of Britain, and abandoning a commitment to the free movement of labor, capital, goods, and services. It has profound implications for Britain’s legal system, which incorporates a large body of regulations that cover everything from product safety to digital privacy, and for Britain’s economy.

The main ways in which the change will be felt are on trade — Britain will lose automatic access to the European single market — and on immigration, with Britain no longer bound to allow any EU citizen to live and work in the country. Britain will have to try to negotiate new deals covering those ­issues.

To those in Britain who supported remaining in Europe, the result of Thursday’s in-or-out referendum was a painful rejection, leaving the country exposed to a possible economic downturn and signaling a step away from the multiculturalism that they say has made Britain among Europe’s most vibrant societies.

To backers of leaving, the outcome was vindication of their belief that Britain could pursue an independent course in the world, free of the Brussels bureaucracy and able to control the flow of immigrants into the country.

“Dare to dream that the dawn is breaking on an independent United Kingdom,’’ Nigel Farage, the leader of the UK Independence Party, one of the primary forces behind the push for a referendum on leaving the European Union, told cheering supporters just after 4 a.m.

For Cameron, the results were a humiliating disaster, forcing him to announce his departure only 13 months after he won reelection behind a surprisingly large Conservative majority in national elections. Critics said he had led Britain out of Europe for no good reason and that the unity of the United Kingdom itself was threatened, with Scotland now more likely to try again to bolt.

Scotland voted by 62 percent to 38 percent to remain in the European Union, and the Scottish first minister, Nicola Sturgeon, said Friday that it was “democratically unacceptable’’ for Scotland to be dragged out of it against its will. Another independence referendum, she said, “is now highly likely.’’

Speaking in front of 10 Downing Street early Friday, with his wife, Samantha, standing nearby, Cameron said he would resign once a new leader had been chosen by his party, a decision he expected by October. He will stay now to provide stability, but a new prime minister, he said, should formally begin Britain’s withdrawal from the European Union and negotiate the terms of that divorce.

“I held nothing back,’’ Cameron said. His voice breaking, he said, “I love this country and I feel honored to have served it.’’

His statement created an immediate churn in the political waters, with speculation that the two Conservatives most likely to succeed him are Boris Johnson, the flamboyant former mayor of London who helped lead the Leave campaign, and Theresa May, the Home secretary, who supported Cameron and Remain, but concentrated on doing her job rather than campaigning.

The immediate market reaction was an effort to find a floor in the midst of so much uncertainty, said Barrington Pitt Miller, an equity research analyst at Janus Capital. But he said he expected British economic growth to be zero or negative in the short and medium term, with a secondary impact over time as London’s financial services sector, which makes up about 10 percent of the economy, begins to move staff and headquarters to Frankfurt, Paris, or Dublin.

A lot will depend on how the EU chooses in the end to respond — whether it is “vindictive, friendly or frightened,’’ he said.

Johnson and some in the Leave campaign argued that the other European nations valued trade with Britain so much that they would negotiate a special deal after Britain’s withdrawal to let Britain remain in the single market without having to guarantee freedom of movement and labor. That seems highly unlikely, because it would only encourage other nations to pressure Brussels. But it may be that as the dust settles, some sort of association agreement with Britain could be negotiated, as Merkel suggested on Friday, though the price could be high.