Roger Rumpf, a peace activist who spent years in Laos and drew international attention to the problem of unexploded bombs from the Vietnam War era, died April 9. He was 68. (Roger Arnold)

Over a period of about 10 years during the war in Vietnam, more than 2 million tons of explosive ordnance fell from U.S. planes on the lush neighboring nation of Laos — a campaign intended to choke off the Ho Chi Minh trail used as a supply route by the North Vietnamese and Viet Cong. According to United Nations statistics, Laos became, per capita, the most heavily bombed country in history.

Some of the miniature bombs looked like fruit, a design intended to entice the enemy in a war that ended nearly four decades ago. A farmer’s hoe is enough to set one off; so is a misstep by a grazing cow. Children mistake the “bombis,” as they are known, for toys.

Roger Rumpf, who died April 9 at 68 on his farm in Warrensburg, Mo., dedicated nearly his entire adult life to Laos — and to keeping that country in the American consciousness as memory of the Vietnam War faded. For years he was a sort of unofficial U.S. ambassador in Laos and a prominent advocate in Washington for Laotian issues, particularly the problem of the leftover unexploded bombs that continue to maim and kill.

His death, from leukemia and acute myelodysplastic syndrome, was confirmed by his wife, Jacquelyn Chagnon.

Peace had been a concern in Mr. Rumpf’s family for generations. His German ancestors came to the United States in the 19th century in part to avoid conscription in the military. His parents stood out in their farming community during the racial tension of the civil rights era — they read Ebony magazine, Chagnon said, and hired African Americans at a time when many other whites did not.

During the draft for the Vietnam War, Mr. Rumpf went before his draft board and described himself as a conscientious objector, his wife said. By the early 1970s, both had joined an initiative called the Indochina Mobile Education Project — a traveling exhibit created to educate Americans about the people of Indochina and how the Vietnam War had affected them.

Mr. Rumpf first went to Laos in 1978, three years after the war ended. The American Friends Service Committee, the Quaker social justice organization, had selected him and Chagnon as co-field directors for operations in Indochina.

“It was such a stark thing,” said John Cavanagh, an activist who worked with Mr. Rumpf in the 1970s and today is director of the Institute for Policy Studies in Washington. “Everyone else is coming home,” Cavanagh said, referring to U.S. military personnel, “and here [were] Roger and Jacqui going in the other direction.”

They stayed in Laos until 1982, then returned in 1986 for another four years.

During the second tour, the New York Times reported that the entire unofficial U.S. aid program in Laos consisted of four people — Mr. Rumpf and his wife and another couple representing the Mennonite Central Committee. There was no official aid program.

Mr. Rumpf and his wife lived on the Mekong River in the capital of Vientiane. They quickly understood the severity of the dangers created by unexploded ordnance, known as UXO.

“It’s hard for Americans to understand,” Mr. Rumpf told Round Earth Media years later. “You walk down a path, you move anywhere, you gotta look down . . . you gotta watch what you’re stepping on, and you’ll probably be stepping on a few underneath the ground.”

Among other efforts, Mr. Rumpf helped bring cattle to farmers who had lost their livestock to explosions, Chagnon said. He worked on irrigation projects, including one that killed 11 people, his wife said, when undetected bombs exploded. He helped coordinate initiatives to collect and distribute shovels, which are less likely than hoes to detonate bombs hidden in the earth.

Back in the United States, Mr. Rumpf worked to raise awareness about UXO. U.S. officials had volunteered to sweep the country, the Times reported in 1987, but the Communist-controlled Laotian government declined help from the United States.

In recent years, diplomatic relations with Laos have improved. The U.S. government provided $9 million for unexploded ordnance removal in Laos in 2012, according to the State Department, an increase from $5 million in previous years. Last July, Hillary Rodham Clinton became the first U.S. secretary of state to visit Laos since the Vietnam War era.

“It was through the efforts of people like Roger and Jacqui that eventually the magnitude of the [UXO] problem became known,” said Angela Dickey, a State Department fellow at the U.S. Institute of Peace. “He and Jacqui should be given a great deal of credit.”

Mr. Rumpf was an “extraordinary person,” said William Goodfellow, executive director of the Center for International Policy, and “really made a difference in Laos.”

Roger Erwin Rumpf was born Oct. 26, 1944, in St. Joseph, Mo., and grew up on his family’s farms. He received a bachelor’s degree in history from Elmhurst College in Illinois in 1966. In 1969, he received a master of divinity degree from the Eden Theological Seminary in Webster Groves, Mo., and was ordained a minister in the United Church of Christ.

Mr. Rumpf joined the mobile education project, his wife said, because he did not think he was suited for a traditional ministry and wished to pursue social justice work. He made his longtime home in Washington, when he was not in Laos, and returned to Missouri in 1997.

Survivors include his wife of 38 years, Jacquelyn Chagnon of Warrensburg; a daughter, Miranda Rumpf of Warrensburg; and two sisters.

In Laos, Mr. Rumpf and his wife unofficially adopted a 10-year-old boy, Joey Khampaseuth, who Chagnon said had been abandoned and lived on the streets. Now 22, and residing in the Lao capital, he, too, survives.