We seem to live in an era of massacres. More than 500,000 Tutsis were hacked to death by their Hutu ethnic rivals in Rwanda in 1994. The following year, more than 8,000 Bosnian Muslims were shot to death by the Bosnian Serb army at Srbrenica. In Syria, more than 100,000 are dead, and more keep dying in massacres large and small by bullet, shell, bomb and poison gas.

Now Gary J. Bass, a journalist and professor of politics and international affairs at Princeton, has come forth with “The Blood Telegram,” a profoundly disturbing account of the hitherto hidden role of Richard Nixon and Henry Kissinger in the slaughter of hundreds of thousands of inhabitants of East Bengal (subsequently the nation of Bangladesh) and the making of 10 million refugees during Pakistan’s civil war in 1971. Apparently no precise figure is available for the deaths, but Bass cites a CIA and State Department estimate of about 200,000 midway through the killing.

The partition of British India in 1947 into mainly Hindu and mainly Muslim areas created a bifurcated Pakistan in a bizarre configuration that was a recipe for political instability and military dictatorship. West Pakistan was forged from the Muslim-dominated provinces on the western side of the subcontinent, while East Pakistan was created on the other side from the chiefly Muslim province of East Bengal. Roughly 1,000 miles of India lay between. East and west shared virtually nothing except religion.

Serious trouble began in 1970 when the president of Pakistan, Gen. Agha Muhammad Yahya Khan, permitted a national election. The winner was a charismatic Bengali leader named Sheikh Mujib-ur-Rahman and his Awami League. Mujib enraged the army leadership, whose troops were drawn almost entirely from the Punjab and other western provinces and had no affection for the Bengalis, by publicly advocating autonomy for both wings under a federal system, while privately promoting secession and independence for East Bengal.

“The Blood Telegram: Nixon, Kissinger, and a Forgotten Genocide” by Gary J. Bass. (Knopf)

On the night of March 25, 1971, Yahya Khan launched a ferocious crackdown. The orgy of murder, rape and mayhem went on for months, focusing in genocidal fashion on the minority of Bengali Hindus regarded as most friendly to Pakistan’s enemy, India.

Nixon and Kissinger, his national security adviser, have sought to draw a curtain of silence over their role by omitting or glossing over the atrocities in their memoirs. Bass has defeated the attempted coverup through laborious culling of relevant sections of the Nixon White House tapes, declassified State Department documents and interviews with former officials, American and Indian, who were involved.

Archer Blood, the U.S. consul general in 1971 in Dhaka, the principal city of East Bengal, and his staff were horrified by the violence. Their reports to the State Department in Washington described the killings in gruesome detail and urged the strongest possible intervention to try to bring the carnage to an end. Pakistan’s generals were highly susceptible to pressure from Washington. Virtually their entire military, from the F-86 Sabre jet fighters in the air force to the armored, artillery and infantry contingents, was equipped with American weaponry and depended on the United States for the ammunition and spare parts required to keep it operating.

But the consulate’s cables met with what Blood later called a “deafening” silence from Washington. With the Bengalis being killed by American weapons wielded by an American-sponsored army, and Washington doing nothing to try to stop it, the United States had become complicit in the massacre.

In desperation, Blood’s younger staffers drew up a “dissent cable,” a Vietnam War-initiated reform in the Foreign Service meant to allow diplomats to speak out, confidentially but frankly, against official policy. Bass calls it “the Blood telegram” after its most important signatory — and as a double-entendre title for the events the book recounts. The cable accused the Nixon administration of “moral bankruptcy” and demanded action to stop the murders “in order to salvage our nation’s position as a moral leader of the free world.” Twenty members of the consulate staff signed the cable, a “roll call of honor,” as Blood put it. As the senior man, he had the most to lose by signing, and lose he did in the years to come.

What Blood and his young associates did not know was that Nixon and Kissinger were using Yahya Khan as a secret communications channel to Mao Zedong’s China. It was Yahya Khan who would arrange Kissinger’s clandestine trip to China in July 1971 to prepare the way for Nixon’s epochal visit there in February 1972. Nixon and Kissinger were determined to let nothing interfere with their enterprise to checkmate the Soviet Union in the Cold War by turning China into a friend of the United States. The cables from Blood’s consulate about this inconvenient massacre in East Bengal infuriated both men.

And there was more stroking their anger. They loathed India because the Indians had adopted a neutral position in the Cold War and then turned to the Soviet Union to obtain weapons, which they could not get from the United States, to fight Pakistan. To Nixon, the Indians were “a slippery, treacherous people.” To Kissinger — who comes across as a cold-blooded practitioner of realpolitik given to rages when he doesn’t get his way — the Indians were “insufferably arrogant,” with “convoluted minds.” At one point on the tapes, Nixon remarks, “The Indians need — what they really need is a” — Kissinger interjects, “They’re such bastards.” And then the president finishes his thought: “a mass famine.”

Nixon had a particular animus, a dislike that was mutual, toward Indira Gandhi, the prime minister and daughter of Jawaharlal Nehru, a founder of India and its first prime minister and greatest statesman.

Rather than seeking to restrain the Pakistani military, Nixon and Kissinger did all they could to strengthen it for the open clash with India that loomed because of the bloodshed in East Bengal. Once the fighting started, Bass recounts that, in a precursor to Watergate, the two men knowingly broke U.S. law by approving the transfer to Pakistan of American-supplied F-104 Starfighter jet interceptors from Jordan and Iran, then still under the rule of Shah Mohammad Reza Pahlavi. John Mitchell, Nixon’s attorney general and subsequently one of the major figures convicted in the Watergate scandal, was in the room at the time of the decision and made no objection. In the end, the Indian army decisively defeated the Pakistani forces, liberating East Bengal and fostering the birth of Bangladesh.

After reading Bass’s account of this shameful episode, one has to ask if preservation of the secret conduit to China via Pakistan was worth the lives of more than 200,000 Bengalis. Mao clearly wanted to do business with the United States, and some other channel presumably could have been found. One has to conclude that where the Bengalis were concerned, Kissinger and Nixon simply did not give a damn. And one has to wonder too, what had happened to the America that once stood for liberty, justice and decency.

Neil Sheehan, who spent three years in Vietnam as a war correspondent, is the Pulitzer Prize-winning author of “A Bright Shining Lie: John Paul Vann and America in Vietnam” and “A Fiery Peace in a Cold War: Bernard Schriever and the Ultimate Weapon.”