Others blame extremist monks; one of their most charismatic leaders, U Wirathu, has been called “the Burmese Bin Laden” because of his video sermons urging attacks on Muslims and boycotts of their businesses. His hateful incitement goes unchecked, and photographs on social media sites have even shown him receiving alms from hard-liners.

The sowers of hate have rich soil in which to work, but it wasn’t always so.

Muslims began arriving in Burma as traders and mercenaries in the 13th century and lived alongside Buddhists in relative peace for centuries. In the 19th century, under the reformist King Mindon, mosques were built and thousands of Muslims served in Burmese infantry and artillery divisions. Mindon even helped build a hostel in Mecca for Burmese Muslims making the pilgrimage, or hajj.

The seeds of sectarian conflict date from British rule, which started in southern Burma. Indian immigrants flocked there after the first Anglo-Burmese War, from 1824 to 1826. Later, after two more wars that made Burma a province of colonial India, riots erupted, targeted at Indian Muslims who had come to dominate low-skill jobs and money-lending. In some of the worst clashes, in 1938, hundreds of Muslims and Buddhists were killed, and mosques were destroyed.

Nevertheless, Muslims achieved prominence as student activists, politicians, army officers, civil servants, scholars and teachers. U Razak, a Muslim cabinet minister, was assassinated alongside the independence leader Aung San — Ms. Aung San Suu Kyi’s father — in 1947. But the situation for Muslims worsened after the military seized power in 1962.

The regime sought to impose ethnic purity by marginalizing minorities (ethnic Burmans make up only two-thirds of the population) and non-Buddhists. Eventually, even traditional Buddhists were marginalized, as dictators employed a grotesque parody of their religion to manipulate the masses. The leaders portrayed themselves as devout, but showed no compassion in brutally repressing minorities and dissidents.

Today’s Buddhist extremists are the legacy of this policy. They are everywhere: on the streets and in Parliament, wearing military fatigues, business suits and monks’ robes. Some monasteries have become breeding grounds for extreme nationalism. Many senior monks are corrupt, including those in the state-sponsored Buddhist council, the Sangha.

President Thein Sein and Ms. Aung San Suu Kyi, former rivals, share some responsibility for the violence and have a legal and moral duty to act. Freed after more than a decade under house arrest, Ms. Aung San Suu Kyi, now a member of Parliament, has called for the rule of law, but this is not enough. To be as respected as Mohandas K. Gandhi and Nelson Mandela, she must explicitly condemn the bloodshed against Rohingyas, Kachin and other minorities and criticize the police and security forces for their negligence and complacency. Newspapers, newly freed from censorship, must cease their jingoistic sloganeering and assume the responsibilities that come with liberty.

Machete-wielding monks and militants, implicitly granted a license to kill, have been a blot on our nation and the government’s recent commitment to change. If President Thein Sein does not move quickly to stop the bloodshed, a historic opportunity for peace — and acceptance for Myanmar in the community of nations — will be lost.