In May 2016 when I was Japan's ambassador to the United States, then U.S. President Barack Obama visited Hiroshima, while in December of that same year then Japanese Prime Minister Shinzo Abe visited Hawaii's Pearl Harbor.

File photo taken May 27, 2016, shows then Japanese Foreign Minister Fumio Kishida (R) giving an explanation regarding the Atomic Bomb Dome in Hiroshima to U.S. President Barack Obama (C) and Japanese Prime Minister Shinzo Abe. (Kyodo)

These locations represented both the start and end points, albeit in reverse, of the tragic war between the two countries, and the mutual visits by the respective leaders were seen as a symbol of reconciliation.

For two former enemies to carry out the rituals of political reconciliation, it takes time to yield results of "substance."

With increased engagement and investment in the United States, Japan's economic advances have become less contentious on the other side of the Pacific, and the relationship has solidified through cooperation on security agreements as well as at grassroots levels.

It was important that Japan, which had been criticized for taking a free ride, made it possible to support the United States in the event of an emergency on the Korean Peninsula and has permitted limited exercise of the right to collective self-defense.

There was strong opinion that Mr. Obama, who won the Nobel Peace Prize for advocating for a "world without nuclear weapons," should visit Hiroshima, while he had expressed a desire to do so from an early stage.

On the other hand, some in the United States were more cautious of a reciprocal visit with the conservative Abe administration.

However, in a speech to U.S. Congress in April 2015 with former American prisoners of war listening on, Mr. Abe left a strong impression by saying that he would move forward while directly confronting the reality of WWII. He said both countries had overcome the scars of the past.

I also believe that the discourse that marked 70 years since the end of WWII in August that same year set the conditions for the diplomatic visits to occur without resistance, like a ripe persimmon falling from its tree.

The most memorable part for me of Mr. Obama's visit to Hiroshima was the very natural way in which he embraced a survivor of the atomic bombing.

Then Japanese Prime Minister Shinzo Abe (L) and U.S. President Barack Obama release flower petals into the sea at the USS Arizona Memorial at Pearl Harbor in Hawaii on Dec. 27, 2016, to commemorate those who died in the Japanese surprise attack in 1941. (Kyodo)

An apology was unimportant at that stage when the mutual understanding between Japan and the United States had deepened to that extent.

Mr. Abe then decided on his own to visit Pearl Harbor, knowing that it was the right time, before the end of Obama's tenure, to respond to the act of reconciliation.

No country can forget the experience of a nation-consuming war.

It has been pointed out that it is a contradiction that Japan, which aims to abolish nuclear weapons, is protected by the U.S. nuclear umbrella.

But it is also the result of a choice as a country that has been the victim of a nuclear bombing to never repeat such an attack.

Japan, which lost the war, must be smart enough to cope with the harsh reality that neighboring countries are strengthening their nuclear capabilities, while still championing the ideal of the abolition of nuclear weapons.

Japan is fated to be an ally of the United States from its place in Asia.

In order for Japan to continue to demonstrate leadership in the region, it will have to confront the process of reconciliation with countries like South Korea.

It is also a strategic requirement, although Japan-South Korea relations are yet to have the "substance" that those of Japan and the United States have.

To achieve this, both countries must have a long discussion that identifies the limits of their tolerance, while accepting their sentiments about the past along with the willingness of their leaders to do so.

(Kenichiro Sasae was born in Okayama Prefecture, western Japan, in 1951. After serving as director general of the Foreign Ministry's Asian and Oceanian Affairs Bureau and vice foreign minister, he was Japan's ambassador to the United States from 2012 to 2018. He now serves as president of the Japan Institute of International Affairs.)

Kenichiro Sasae is pictured in Tokyo on Nov. 24, 2021. (Kyodo)