America still bears the scars of the Vietnam War, the longest conflict in its history up to that time. At the height of the war more than 500,000 U.S. troops were involved in the fighting, which killed more than 58,000 Americans and wounded 303,000 over the course of a decade. Among the Vietnamese the casualties were even more horrific: Some 3.5 million soldiers and civilians were killed or wounded during the conflict. It was a bloody legacy that both countries have struggled to overcome in the years since the war ended in 1975.

That is why President Barack Obama is seeking to open a new chapter in relations between the two countries during his visit to Hanoi this week by announcing an end to the 50-year ban on American arms sales to Vietnam. By doing so, the president aims to end one of the last legal vestiges of the Vietnam War and build on efforts over the last two decades to normalize relations with our former adversary.

Mr. Obama was careful to emphasize that his decision to lift the arms embargo against Vietnam was not aimed at China, whose territorial claims and growing military might in the South China Sea have alarmed neighboring countries in the region. Instead, the president characterized strengthening relations between the U.S. and Vietnam as part of his strategic “pivot” to Asia and as a signal of U.S. commitment to retain a robust presence in the region. The move is designed to bring us closer to one of the world's fastest-growing economic zones and complement the Trans-Pacific Trade Agreement Mr. Obama wants Congress to approve.

Lifting of the arms ban against Vietnam doesn't mean Hanoi will get unfettered access to American weapons. The U.S. will still review future sales on a case-by-case basis to determine which arms are appropriate and which are not. Moreover, American officials remain concerned over Hanoi's human rights policies, which are oppressive. The U.S. hopes to use any arms sales to Vietnam as a carrot to nudge it toward reforming its Communist, one-party government and embracing free-market principles. Washington also wants to signal to other Southeast Asian nations that America is still the pre-eminent power in the Pacific and that they can benefit from stronger economic and military ties with us.

Nobody is expecting that to happen overnight. But as one of the largest and most economically vibrant countries in the region, Vietnam could serve as a model for other nations struggling to make the difficult transition from single-party authoritarian regimes to more open, democratic governance and markets that recognize the importance of greater accountability and transparency in global trade. The U.S. should be prepared to provide every assistance possible to help governments in the region liberalize their societies in ways that contribute to expanded economic growth and democratic freedoms.

The president is well aware that there are plenty of examples of the opposite trend at work in the world today, including a resurgent Russia and its newly assertive president, Vladimir Putin. The countries of Southeast Asia are deeply suspicious of developments in Moscow as it seeks to undermine the post-Cold War order through aggressive military interventions in Ukraine, Georgia, Kosovo and Syria. They need America's assurances that it will be a counterbalance not only to China, their giant neighbor to the north, but to Russia as well.

Even so, if the U.S. doesn't cultivate closer relations with Vietnam, it could become closer to Russia anyway, if only because Hanoi fears becoming drawn ever more deeply into China's orbit. Mr. Obama clearly wants to keep that from happening, and we think giving Hanoi an alternative in the form of better relations with a U.S. is the most effective way of accomplishing that.