For years after US forces left Vietnam, following a conflict that had killed millions in Southeast Asia, the two countries didn't speak.

Diplomatic relations were finally restored in 1995 by President Bill Clinton, but on Monday President Barack Obama went a step further: During a visit to Hanoi, he announced he was lifting the embargo on US companies selling arms to Vietnam, 41 years after the fall of Saigon.

The Vietnam War was the bloodiest conflict America has been involved in since World War II. The physical and mental scars are still there for many of the Americans who served.

But on Monday Obama pointed to Secretary of State John Kerry, who served in the Vietnam War, and said veterans on both sides had shown “hearts can change, and peace is possible.''  

Republican Senator John McCain has been a big advocate for lifting the arms embargo. McCain was a prisoner of war in North Vietnam for five years, and was tortured.

Vietnam will be the first communist nation to be supplied with US weapons since World War II, when President Franklin D. Roosevelt sent arms to the Soviet Union to help fight Hitler.

“People that have been paying attention to this issue have seen it coming," says The World's Patrick Winn, who covers Southeast Asia from his base in Bangkok and has written about the embargo. "We just didn't think it was going to happen so soon.”

“It’s pretty obvious the US and Vietnam are moving closer and closer together,” says Winn. “They are driven by a common goal, and that’s to thwart the rise of China, particularly China’s dominance of the South China Sea.”

“China regards the entire Sea as its own aquatic backyard,” explains Winn, “and the US would like to make sure that China doesn’t dominate this really important waterway.”

Obama said the US wants to help Vietnam defend itself. “But to defend itself against who?” asks Winn. “I think the answer is China.”

China supported North Vietnam for much of the war with the United States. But China and Vietnam fought their own brief but bloody border war in 1979, and relations have been difficult ever since.

Obama denied the lifting of the weapons embargo was directed against anyone, and China issued a public statement welcoming the end of the Cold War-era restriction. But Winn says the move will “heighten tensions down the road, for sure.”

The deal has been criticized by Human Rights Watch. "In one fell swoop, President Obama has jettisoned what remained of US leverage to improve human rights in Vietnam — and basically gotten nothing for it," said a statement from Human Rights Watch’s Asia director, Phil Robertson.

Obama said every future weapons deal would be closely scrutinized, and that Washington would be keeping an eye on human rights in Vietnam. That was not enough to satisfy critics.

“But let’s get a reality check,” says Winn. “US weapons are not going to start flooding into Vietnam.” Vietnamese forces are currently largely equipped with Russian and Soviet-era weapons, which are incompatible with US systems. US weapons are also comparatively pretty expensive, and Vietnam does not have deep pockets.

The most likely sales are specialized surveillance equipment, says Winn. 

From PRI's The World ©2016 PRI