Vientiane, Laos (CNN) Secretary of State John Kerry arrived in Laos on Sunday ahead of a major push by the Obama administration to fix a decades-old wrong: clearing up leftover Vietnam-era U.S. bombs.

Kerry's visit will help usher in a new partnership with a former wartime foe and end a dark American legacy that has lingered since the end of the Vietnam War. It also comes ahead of next month's summit in Sunnylands, California, between President Barack Obama and 10 Southeast Asian leaders, and a landmark trip by the President to Laos this fall.

While there, the President is expected to announce a major initiative to help clear leftover Vietnam-era bombs, aides told CNN.

After decades of estrangement and suspicion, relations between the tiny, Communist-ruled country and the United States have improved under Obama. Three years ago, Kerry's predecessor, Hillary Clinton, was the first secretary of state to visit Laos since 1955.

In recent years, the Obama administration has increased programs to help Southeast Asian countries along the Mekong River -- Cambodia, Laos, Thailand and Vietnam -- by improving their infrastructure, health and education systems while quietly expanding U.S. influence in the region as a counterweight to China.

But for Laos, Washington's forward-looking regional agenda is held hostage to its prior actions. While then-Navy Lt. Kerry was serving in Vietnam, the CIA led a bombing campaign next door in Laos as part of what was dubbed the "Secret War."

How it started

From 1964 to 1973, U.S. warplanes dropped more than 2 million tons of bombs on Laos. An estimated 30% of the ordnance failed to detonate, which has led to countless casualties that continue to this day -- at a rate of about 50 per year, according to the Legacies of War advocacy group's statistics.

In May 2012, three children aged 9 to 10 were digging for bamboo when a cluster bomb exploded. One of the children was paralyzed, another killed.

The bomb was just one of more than 75 million unexploded cluster bombs that litter Laos' forests, rice fields and villages, by Legacies of War's calculations. Cluster munitions split open before impact and scatter hundreds of smaller bomblets over a wide area. Many of these bomblets failed to explode on contact and remain hidden for decades, only to maim or kill civilians.

Heavy costs

More than 20,000 people have died at the hands of these remains of cluster munitions in Laos and an estimated 12,000 more victims are in need of assistance, Legacies of War has found.

The U.S. spent $2 million ($17 million in today's dollars) per day for nine years to bomb Laos, but only an average of $4.2 million a year for clearance of unexploded ordnance and victims' assistance over the past 20 years, according to Legacies of War.

In 2010 Congress mandated that the U.S. government give at least $5 million for unexploded ordnance removal. While it was one-third of the $14 million Laos receives each year for clearance from all donors, it was significantly less than the $145 million the U.S. spent for clearing Afghanistan and Iraq.

Since then, funding has been steadily rising. This year, Congress allotted $19.5 million for unexploded ordnance clearance in Laos, thanks in large part to Vermont Sen. Patrick Leahy -- the top Democrat on the Senate appropriations subcommittee for foreign operations and a leading voice in pressing America to live up to its painful wartime past.

"Sen. Leahy feels we have a moral responsibility to deal with it because we created the problem," said Tim Rieser, Leahy's top foreign policy aide and key player in pushing for more funding. "It makes no sense to go at a snail's pace when innocent people are being maimed and killed."

The slow, painstaking process of de-mining has never been a sexy issue. Moreover, so-called "legacy" issues of wars like the one in Vietnam are overshadowed by current events. In Asia, major political and economic relationships with close allies like South Korea and Japan and major powers like China suck up most of the attention.

How it came about

Last fall, in anticipation of this year's ASEAN summit in Laos, the President sent one of his most trusted advisers, Deputy National Security Adviser Ben Rhodes, to visit. After shepherding last year's historic rapprochement between the U.S. and Cuba, Rhodes saw a similar opportunity to repair relations with Laos.

He returned to Washington profoundly moved by the scope of the unexploded ordnance problem and convinced clearance was key to helping the impoverished nation better develop its agriculture and economy.

The amount of unexploded ordnance in Laos hinders development and poverty reduction. Laos has less land to build factories, schools and farms on. He told Obama the United States had an obligation to help. Moreover, with Obama making engagement of Southeast Asia a priority, he argued it was smart policy.

The President agreed it was time to try to solve the problem once and for all.

While the exact figures are still being worked out, Rhodes said the President is poised to commit enough U.S. aid during his visit to Laos to help the government eliminate the bulk of unexploded ordnance in the country.

"It's about settling history's account and meeting our responsibility," Rhodes said. "And this president, both because of his willingness to resolve painful issues in U.S. foreign policy and his focus on southeast Asia, is uniquely suited to do that. There is the potential for this to be a truly historic visit."

How to clear the bombs

Cleaning up unexploded ordnance is a slow and dangerous progress, but it's one that is getting easier, thanks to advances in technology and training of those doing the clearance. The Laos government is in the process of mapping out where all of the bombs in left the country exist, informed by records supplied by the Pentagon about where U.S. warplanes dropped them. With a clearer picture, the government can identify priority areas for clearance.

Now it's a matter of resources. Currently only a small team of dedicated State Department officials, government employees and NGO workers in Laos focus on clearance activities, mine risk education and victim assistance.

Pushing for change

One of those NGOs is run by Channapha Khamvongsa. Having fled her native Laos as a refugee at age 7 with her family, she returned as a graduate student to find the country was still plagued by the legacy of the so-called "Secret War" decades ago.

In 2004, Khamvongsa founded Legacies of War to raise awareness and increase financial support for clearance of unexploded ordnances in Laos. Today, she is a leading voice on the issue.

"Laos was not on anyone's agenda," she said. "When I asked officials why the funding was so low, they said it was because nobody asks," she said. "I realized if someone was raising the issue with the U.S. government and members of Congress, we could do something about it."

Teamwork

She has found willing partners in Leahy and aide Rieser, who hope to secure sustained funding of about $20 million per year to put Laos on track to clear most of the country within 10 years.

"The more people working at it, the sooner it will be done," Rieser said. "We can't find every cluster munition but if we get rid of enough of them to reduce the number of casualties to a handful, then the Lao government can manage on its own."

U.S. officials acknowledge that one of the main drivers of funding for unexploded ordnance is the guilt some Americans feel.

"I think this President believes it's never too late," said Khamvongsa, who is "incredibly optimistic" about Obama's visit. "This visit can show that no matter what has been done in the past, there is always a sense that a wrong can be righted and we can do the right thing."