By all accounts, Vang Pao did not lose confidence during those difficult days. “Honor with one another, sympathy for one another, faith for one another, that’s how we survived,” he told me. His American counterparts felt the same. “This guy was like a brother,” said Devlin, the C.I.A. station chief, who worked with Vang Pao from 1967 to 1970. “He was an extremely good leader. He was worshiped by his troops. We all admired him. Respected him. Liked him.” The C.I.A. and Vang Pao had an understanding about what would happen if the war went badly. “I had been told when I went out there to tell the Hmong we’ll back them to the end, and if we have to pull out, we’ll pull them out too,” Devlin told me. But that was not how things worked out. The end came 33 years ago this week, in May 1975. It was a disaster. Saigon had fallen; the final rout of American military and intelligence officers from the war zones of Southeast Asia was nearly complete. The C.I.A.’s last outpost in Laos was its mountain air base at Long Tieng, the hub of the paramilitary operation. Tens of thousands of Hmong gathered at the primitive airstrip, looking for planes. Very few came, for there was no coherent evacuation plan after 15 years of secret missions. As Dan Arnold, the last C.I.A. station chief in Laos, later recounted, authorization for an airlift had to come from Washington. In his words, the request met “delays at the highest political levels.”

The evacuation was abandoned after a chaotic race against time. “Of course, most of the Hmong wanted to fly along with me to Thailand, but they couldn’t because we only had enough aircraft to lift the officers and family members,” Vang Pao said. At least 50,000 Hmong, including many fighters and their families, were left behind in and around Long Tieng even as Vang Pao and his C.I.A. case officer flew to safety. Thousands were killed by the victorious Communists, according to survivors. Tens of thousands fled into the jungle and wound up as refugees in Thailand; many became boat people, cold-war flotsam, forsaken. Vaughn Vang, now a 50-year-old school counselor in Green Bay, Wis., and chairman of the Lao Human Rights Council, an organization seeking to bring attention to the plight of the jungle Hmong, became a teenage refugee when Laos fell to the Communists. “I ran through the jungle for two years,” he said. “We were 260 when we left, and 39 of us made it out to Thailand.”

The luckiest of the refugees made their way to the United States. Their traditions were hunting and gathering; they had been slash-and-burn farmers who cultivated opium as a cash crop, animists who believed in the spirit world. They were not well suited for life in Sacramento. Today more than 200,000 Hmong live in the United States, mostly in California, Wisconsin and Minnesota. More than half are under 18. While many of the second and third generation are adapting to life in America, overall a quarter or more of the Hmong live in poverty and speak little English, if any.

Over the years, Vang Pao and the other Hmong leaders in the United States have by and large sustained themselves by raising money  raising it by raising hope that someday the Hmong would go back to their land. During the cold-war years, he gave stirring speeches about liberating Laos. The promise proved empty. Unlike, say, Miami’s Cubans, the Hmong have no real hope of return. Their survival has depended far more on social services and welfare agencies than on the political dreams of their aging patriarchs.

“Their way of life has been destroyed,” Dick Holm, a C.I.A. officer who served in Laos, wrote in a memoir. “They can never return.” The United States, in his view, “failed to assume the moral responsibility that we owed to those who worked so closely with us during those tumultuous years.” His colleague, Larry Devlin, said, “We let the Hmong down terribly.”

Image Vang Pao, at the Pa Dong base in Laos in 1961. Credit... John Dominis/Time Life Pictures/Getty Images

Thousands of Hmong survive today as refugees in dismal camps in Thailand. Perhaps 1,000 are still on the run in the jungles of Laos itself. Human rights groups, filmmakers and journalists have documented their plight. Though the jungle Hmong are believed to have staged occasional hit-and-run attacks in the past, Amnesty International reported last year that “the jungle-dwellers’ military capacity is all but depleted decades after some Hmong fought in the C.I.A.-funded ‘secret army’ in Laos during the Vietnam War.” The jungle Hmong say they are being slaughtered by Lao military units who hunt them with automatic weapons and rocket-propelled grenades, exacting blood vengeance for the wars of the 1960s and ’70s. Veterans  American and Hmong  of the secret missions in Laos see this struggle as the last battle of the Vietnam War. “The Communists accuse the Hmong of bringing American bombs to Laos,” Vaughn Vang, the Lao human rights advocate, told me. “This country used the Hmong. They trained them how to fight. Now the Hmong are dying because they were allies of the United States.”