The world was reminded how far America's relationship with Japan has come since the terrifying days of World War II when U.S. President Barack Obama embraced one of the survivors of the Hiroshima attack.

Obama became the first sitting U.S. president to visit Hiroshima, paying tribute to the city ravaged by an American atomic bomb at the end of the war.

Over 100,000 people died from the attacks on Hiroshima and Nagasaki, the only times in world history that a nuclear bomb has been used as a weapon of war. Nuclear disarmament has been a top priority of Obama's presidency, and he urged those who heard his Friday speech to continue his mission.

"We remember all the innocents killed in the arc of that terrible war," he said before meeting Shigeaki Mori, a historian who lived through the 1945 bombing of Hiroshima.

Mori isn't just a survivor, though. He's also spent decades advocating for the American victims of the Hiroshima attack.

ASSOCIATED PRESS President Barack Obama hugs Shigeaki Mori, an atomic bomb survivor, during a ceremony at Hiroshima Peace Memorial Park on Friday.

Mori tracked down the families of the 12 American POWs killed in the bombing, learning about their lives and pushing for their names to be added to the city's official memorial. Mori was 8 when the bombs dropped, and considers the Americans victims as much as the Japanese.

“Unless someone speaks for them, their sacrifices would be thrown into darkness," he told Stars and Stripes last year. "I wanted to shed light on those Americans who fell the victims of the bombing just like [the] other 140,000 people.”

The Americans' names were eventually added to the Hall of Remembrance in Hiroshima Peace Memorial Park.

Prior to Obama's trip, Mori told CNN that "I think it is wonderful that he will visit Hiroshima to mourn for all victims of war."

Shuji Kajiyama/AP Shigeaki Mori, right, pushed for the names of American POWs killed in the Hiroshima attack to be added to the city's official memorial.