A once-fringe separatist movement in Alberta (Canada's oil-rich western province) has surged into the political mainstream after hundreds of thousands of residents signed a petition demanding an independence referendum, prompting the provincial government to back the vote. Canadian Prime Minister Mark Carney has warned the push could become Canada's equivalent of Brexit, the 2016 vote that saw the United Kingdom leave the European Union. The crisis is widely described as the most serious challenge to Canadian national unity in decades, raising fundamental questions about the country's political cohesion.