TOKYO (AP) — An American president in Hiroshima. A Japanese prime minister at Pearl Harbor. One longtime taboo has already fallen this year, and the other soon will.

On Dec. 27, Prime Minister Shinzo Abe will visit the Hawaiian U.S. naval base attacked by Japan in 1941. He will be joined by President Barack Obama, who seven months earlier traveled to Hiroshima to pay tribute to the 140,000 people killed there by a U.S. atomic bomb in 1945. The two attacks bookend World War II in the Pacific.

The importance of the visits may be mostly symbolic for two countries that, in a remarkable transformation, have grown into close allies in the decades since they faced off in brutal conflict. At the same time, it's significant that it took more than 70 years for U.S.-Japanese relations to get to this point. The two gestures of reconciliation are in some ways an attempt to sweep out the final ghosts of the war.

"Despite the amicable relationship that the two countries have enjoyed since the end of the Pacific War, deep-rooted negative sentiment has remained in both countries," said Narushige Michishita, a security expert at the National Graduate Institute for Policy Studies in Tokyo. "The Obama-Abe joint visit to Pearl Harbor will change this."

Several factors have helped both Obama and Abe step in hallowed places their predecessors did not:

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TIME HEALS

For young Americans, Pearl Harbor is an event in history textbooks, but Japan is more likely to conjure up images of manga and sushi. Japanese students learn about the atomic bombings of Hiroshima and Nagasaki, but the message is not to hate America but to prevent such a tragedy from happening again.

"The amount of time passed is an important factor," said Tsuneo Watanabe, a senior research fellow at the Sasakawa Peace Foundation in Tokyo.

"As survivors become fewer, the event becomes part historical memory," said Tosh Minohara, a U.S.-Japan expert at Kobe University in Japan.

To the mix, he added the concern in the U.S and Japan about China's emergence as a military power in the Pacific.

"I think the appearance of a new potential adversary also made this possible," he said. "The U.S. will have to depend on Japan more and more."

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ODD COUPLE

Obama, a liberal Democrat, and Abe, a relatively staunch conservative, seem unlikely partners for this dance.

On a 2014 visit to Japan, Obama was described by the Japanese media as "businesslike," in contrast to Abe, who was said to be looking to develop a personal bond with the American leader.

Their interests dovetailed over Hiroshima. For Obama, a world without nuclear weapons is a stated if unachieved goal, and Hiroshima was a powerful place to deliver that message one more time in the last year of his presidency.

Abe could bask in the limelight as the Japanese leader who brought an American president to Hiroshima, a visit long hoped for by survivors of the atomic bomb and widely welcomed by the public.

At the time, Abe said he had no "specific plan" to visit Pearl Harbor, sidestepping suggestions that reciprocity was called for.

However, in announcing his visit to Pearl Harbor on Monday, he revealed that he has been thinking about the importance of a visit and reconciliation for more than a year, and that he and Obama finalized it when they met at a G-20 meeting in Peru last month.

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CONSERVATIVE CRED

Some American conservatives and military veterans opposed Obama's visit to Hiroshima, but he rode out the storm.

In contrast, Japanese conservatives have been relatively quiet about Abe's planned visit to Pearl Harbor, and even supportive. The right-leaning Sankei newspaper called it "an attempt to end the postwar era" and move beyond "a framework of winners versus losers."

It helps that Abe is a conservative himself. He also faces few political challengers after holding onto office for coming on four years, making him the fourth-longest-serving prime minister since World War II.

"He gets understanding from his conservative supporters, who give him credit for his ... policies," Watanabe said. "A visit to Pearl Harbor by a liberal leader would have been more difficult."

Obama's visit to Hiroshima also helped in a society in which gift-giving and favors should be reciprocal.

"In a way, it was only appropriate," Minohara said.