In the meantime, Nixon sent his national security adviser Henry Kissinger to meet in secret with North Vietnamese negotiator Le Duc Tho, without a representative from South Vietnam present. The two men met for two years without reaching an agreement, and the situation appeared to worsen when the North Vietnamese launched an attack on March 30, 1972, known as the Spring Offensive. The North Vietnamese sent 120,000 troops across the border into South Vietnam in three waves—in the northern provinces, along the central highlands, and into the Mekong delta near Saigon. Only 70,000 U.S. troops remained in South Vietnam, of which only 6,000 were combat troops. The South Vietnamese army had more than 1 million soldiers, yet it still took them nearly six months to push the North Vietnamese back. They would have failed utterly if the United States had not supplied advisers...