"When I testified against the war in Vietnam for the Senate, I spoke of the determination of veterans to undertake one last mission, so that in 30 years when our brothers went down the street without a leg or an arm and people asked, 'Why?', we'd be able to say, 'Vietnam,' and not mean a bitter... not mean a bitter memory, but be instead the place where America turned, and where we helped it in the turning," Kerry said during his keynote address at a summit examining the war and the lessons from it at the Lyndon Johnson Presidential Library in Austin, Texas.
Kerry won a Bronze Star, a Silver Star and three Purple Hearts for his service as a Navy lieutenant during two tours fighting in Vietnam. But then after he left the military, he became one of the most famous opponents of the war leading a 1971 Washington protest against it and testifying before a hearing of the Senate Foreign Relations Committee calling the war "barbaric."
Later as a U.S. senator from Massachusetts he would work for 10 years to help the U.S. normalize relations with Vietnam.
"It has been 45 years since that testimony, but it is clear that we have turned some very important corners. There are hard choices still to make for our relationship to reach its full potential, but now we can say definitively, because so many Vietnamese and Americans themselves refuse to let our past define our future, Vietnam, a former adversary, is now a partner with whom we have developed increasingly warm, personal and national ties."
Kerry added, "That is our shared legacy, and is one that I hope we will continue to strengthen in the years to come. "
The secretary of state will accompany President Barack Obama next month when he travels to Vietnam. as the two countries continue to advance their relations.
Kerry talked Wednesday about how the two nations now cooperate on security matters, how the amount of trade has grown and a large increase in American visitors to the country -- signs of how far relations have come. But he also talked about differences the two countries still have.
Kerry said he sees reminders of the conflict and keeps the memory of Vietnam on his mind as he tries to find solutions in strife-torn countries like Syria and outlaw states such as North Korea, or the fight against ISIS or Boko Haram.
"I mean I don't think any veteran will tell you there aren't moments where there's a flash of some, you know, of some, memory or someone that you remember or something. You know I just lost one of my crew members, you know, a few weeks ago, and all my crew guys were in touch with me and, back with them, and some of them that were just very, very, you know, moved by that, but it just really grabbed them. And I think that it stays with you."
During the Wednesday session, moderated by documentary producer Ken Burns, Kerry for the first time talked publicly about one trip back to Vietnam while he was working on the normalization issue. He was meeting with the Vietnamese president and chairman of the communist party trying to persuade them to let him go underneath the tomb of former leader Ho Chi Minh because of some concerns some missing American MIAs might be there.
"You can imagine" the reaction, Kerry said. "It was pretty amazing." He got the approval and went down but didn't find anyone.
The three-day summit in Austin also included a speech Tuesday by former Secretary of State Henry Kissinger, who served in the administrations of Richard Nixon and Gerald Ford and an appearance by anti-war activist Tom Hayden.
Library president Mark Updegrove said since the war was such an instrumental part of the presidency of Lyndon Johnson it was important to examine its impact.
"In keeping with President Johnson's vision for his library, we will take an unvarnished look at the most controversial fact of his presidency," Updegrove said. "Our goal is to shed definitive light on the Vietnam War, its lessons and legacy."
CNN's Katelyn Newman contributed to this story.
