Britain’s unprecedented decision to leave the European Union sent shock waves through the country and around the world Friday, rocking financial markets, toppling Prime Minister David Cameron and even threatening the ties that bind the United Kingdom. Britons absorbed the overwhelming realization that their antiestablishment vote has pushed the British economy into treacherous and uncertain territory and sparked a profound crisis for a bloc founded to unify Europe after the devastation of World War II. [...] many Britons signed a petition for a rerun of the referendum on EU membership that they crashed the House of Commons website hosting the document. The decision to leave the EU launches a years-long process to renegotiate trade, business and political links between Britain and what will become a 27-nation bloc, an unprecedented divorce that could take a decade or more to complete. Pro-Brexit voters were persuaded by the argument that leaving the EU meant taking back control of immigration — by abandoning the bloc’s principle of free movement among member states — and reclaiming billions that Britain pays to Brussels each year.