The 1980 meeting between Northern and Southern Vietnamese bishops was the first since Communist forces took control of North Vietnam in 1975.
The Holy See welcomed Iran's historic nuclear deal and expressed hopes that more future breakthroughs be on the horizon on other issues.
Jesuit Fr. Federico Lombardi, Vatican spokesman, said that "the agreement on the Iranian nuclear program is viewed in a positive light by the Holy See."
Francis also said he had not tried coca leaves to deal with the high altitude in Bolivia and admitted that being asked to pose for selfies makes him feel "like a great-grandfather."
Francis Chronicles: "We cannot force anyone to receive us, to welcome us; this is itself part of our poverty and freedom."
Bishops in Paraguay had wanted the pope to meet with small farmers and indigenous people who have been forced off their land.
In Paraguay, Francis told invited dignitaries at a concert that trading votes for favors is "something that happens in every country" and is a form of corruption.
Pope Francis visited one of Latin America's most notorious prisons, calling himself "a man who was and is saved from his many sins."
"I couldn't leave Bolivia without seeing you, without sharing the hope and faith given in the cross," he told people at Palmasola prison in Santa Cruz.
Speaking on the final morning of his less than 48-hour visit to Bolivia, the pope called for conversion and a changing of attitudes among inmates in their relations among each other and the broader society, which often views such populations with suspicions.
In the rousing 55-minute speech, the pope also repeated the church's apology for its role in colonialism of the Americas.
The cross was created by a Jesuit martyr, who was assassinated in 1980 after being active in Bolivia's pro-democracy movement.
The Eucharist calls people to give all they are and have to God, seek his blessing and then take his love to the world, Pope Francis said in Bolivia.