Various armed insurrections by the Rohingya have taken place since the 1940s and the population as a whole has faced military crackdowns in 1978, 1991–1992, 2012, 2015, and particularly in 2016-2018, when most of the Rohingya population of Myanmar was driven out of the country, into neighbouring Bangladesh. By December 2017, an estimated 625,000 refugees from Rakhine, Myanmar, had crossed the border into Bangladesh since August 2017. UN officials and Human Rights Watch have described Myanmar's persecution of the Rohingya as ethnic cleansing. The UN human rights envoy to Myanmar reported "the long history of discrimination and persecution against the Rohingya community... could amount to crimes against humanity", and there have been warnings of an unfolding genocide. Probes by the UN have found evidence of increasing incitement of hatred and religious intolerance by "ultra-nationalist Buddhists" against Rohingyas while the Myanmar security forces have been conducting "summary executions, enforced disappearances, arbitrary arrests and detentions, torture and ill-treatment, and forced labour" against the community.