"In 1969, Chairman Mao had tasked four senior military marshals to study China’s strategic policy. Throughout the spring and summer, Chinese and Soviet armies had been skirmishing. Moscow was debating whether to bomb China’s nuclear arms facilities. That August, Beijing faced a huge new deployment of Soviet forces massing at China’s border at Kazakhstan. At the very moment Nixon was seeking a secret American rapprochement with China, two of the marshals on Mao’s task force, Chen Yi and Ye Jianying, proposed playing “the card of the United States.” Marshal Chen specifically recommended high-level talks with Washington. Mao accepted their report."
"On August 14, 1969, Nixon convened the National Security Council in San Clemente. Those gathered at the Western White House included Nixon, Kissinger, Rogers, Laird, Helms, and Mitchell.
The main subjects were China and the Soviet Union, whose armies were clashing in a border battle and whose leaders had nuclear weapons at hand. Nixon startled his national security team by taking China’s side. Moscow “may have a ‘knock them off now’ policy,” the president said. “We must think through whether it is a safer world with China down.” Nixon believed it was best to see that the largest Communist nation in the world survived.
Nixon’s fear of a cataclysmic clash between China and Russia was a remarkable fore foresight. Four days later, William L. Stearman, the State Department’s ranking intelligence expert on Hanoi, who was about to join Kissinger’s staff, sat down to lunch at a Washington hotel with Boris N. Davydov—officially a diplomat, in reality a spy stationed at the Soviet embassy. Such conversations, often stranger than fiction, were part of the unwritten code of conduct between the Cold War combatants.
“Davydov asked point blank what the US would do if the Soviet Union attacked and destroyed China’s nuclear installations,” Stearman wrote in a top-secret memo that went straight to Kissinger. “What would the US do if Peking called for US assistance in the event Chinese nuclear installations were attacked by us?”
Kissinger called a crash meeting in San Clemente with Attorney General Mitchell, CIA covert operations chief Thomas Karamessines, and the handful of senior State and NSC experts he trusted.
If the border battle went nuclear, “the consequences for the US would be incalculable,” Kissinger said. “We must make this very plain to the Soviets despite the US nuclear policy in Europe,” which included an all-out attack with thousands of nuclear weapons if Soviet troops crossed into West Germany. “It would be helpful to know something about what DEFCON should be entered into,” he added, if “the Soviets were to knock out the Chinese nuclear capacity.” Three weeks later, both the Soviet Union and China conducted nuclear weapons tests. The cataclysm never came, but it was now clear to all that Moscow and Beijing were implacable enemies."
― from "One Man Against the World: The Tragedy of Richard Nixon"