President Barack Obama has announced the US is fully lifting its embargo on sales of lethal weapons to Vietnam, its one-time enemy.
Speaking during a visit to communist Vietnam and talks with its leaders, Mr Obama said the move removed a “lingering vestige of the Cold War”.
He said both sides had “developed a level of trust and co-operation”.
Mr Obama’s visit comes amid warming ties, as the US seeks to build its relationship with its Pacific allies.
Vietnam had been arguing for an end to the arms embargo, which had been in place for decades. It was partially lifted in 2014.
Mr Obama said it was “clear from this visit that both our peoples are eager for an even closer relationship”.
His visit comes 41 years after the end of the Vietnam War in which the US sought to prevent a communist takeover of South Vietnam.
Several million Vietnamese – civilians, communist fighters and South Vietnamese soldiers – were killed, as well as more than 58,000 US soldiers.
By the end of the war in 1975, the communists had gained control of the entire country.
The lifting of the embargo is seen as allowing Vietnam to bolster its defences at a time of territorial disputes with its neighbour China, which was unhappy with a partial relaxation of the ban in 2014.
However, Mr Obama said the lifting of the ban was not based on China but part of a long-term normalisation of ties with Vietnam.
White House officials had indicated the ban would be lifted only if there was an improvement in human rights in Vietnam.
The BBC’s Jonathan Head in Hanoi says that consideration appears to have been put aside and the lifting of the embargo is basically putting to bed all the lingering issues from the Vietnam War.