The bitter past that has divided South Korea from Japan had been a powerful force for years. Despite the repeated efforts of the United States and their mutual ally South Korea, it was impossible to overcome.
South Koreans claim that Japan has never apologized or made amends for the brutal colonial rule it had over the Korean Peninsula between 1910 and 1945. South Korea is often seen by the Japanese as a neighbor who has broken promises and has not kept treaty agreements meant to heal historical wounds.
The thawing in relations has been accelerated by the arrival of two new administrations, in neighboring countries. President Yoon-Suk Yeol of South Korea and Prime Minister Fumio Kishhida of Japan.
In March, both countries took steps to resolve a long-running dispute about forced labor during World War II. In April, South Korea restored Japan as a preferred trade partner. This prompted Tokyo to begin the process of restoring that status for South Korea. Yoon's declaration that Japan should no longer be expected 'to kneel' because of its history 100 years earlier drew attention in his own country.
Now, Mr. Kishida will be making a visit to South Korea in an event that will be closely monitored for any new signs of progress. Here are some global forces that have influenced their mutual outreach.
Tensions with China and Russia
Tokyo and Seoul are aligning themselves closer with Washington, as China is promoting an alternative vision of the World in which the United States holds less power and Russia's invasion into Ukraine has raised alarm over a new age of militarization.
Both countries supported Biden's 'free-and-open' Indo-Pacific vision. They attended a NATO summit last summer, where leaders condemned Russia’s invasion of Ukraine.
The two countries are aware that the rapidly changing geopolitical landscape has brought about challenges they can't handle alone. In recent years, the joint maneuverings of Chinese and Russian aircraft near South Korean airspace and Japanese airspace helped to drive home that message.
Kishida calls South Korea "an important neighboring nation with whom we should work." Yoon encouraged South Koreans not to view Japan as the'militaristic aggressors of the past,' but rather as a 'partner that shares the same values.
In March, Secretary of State Antony J. Blinken stated that the trilateral relationship between South Korea and Japan was "central to our shared vision for a free, open Indo-Pacific Region". This is why he and other senior Departmental colleagues have spent so much time on this partnership.
North Korea's nuclear arsenal
The growing threat of nuclear weapons and missiles from North Korea was an incentive to Seoul and Tokyo for them to realize the strategic importance of trilateral cooperation between the United States and South Korea. North Korea fired missiles at Japan in recent months and also threatened to attack South Korea with nuclear weapons.
South Korea is not formally an ally of Japan, and it has been reluctant to work with them militarily beyond humanitarian missions in the high seas. They are now expanding their military cooperation, mostly because of North Korea.
In November last year, the leaders of Japan, the United States and South Korea met at Phnom Penh in Cambodia to discuss the sharing of real-time North Korean missile alert data. In recent months, the three nations have expanded their trilateral missile defence and other military drills.
Seoul's efforts to repair ties with Tokyo included re-establishing a bilateral agreement on military intelligence sharing that assists the two neighbors in guarding against North Korean missiles.
Global supply chains are vulnerable
In the same year 2019, Japan placed restrictions on the export of chemicals vital to South Korea's semi-conductor industry. Seoul filed a complaint with the World Trade Organization against Tokyo. Both nations removed one another from their "white list" of preferred trade partners.
Seoul and Tokyo have also agreed to begin an "economic security dialogue" to discuss the cooperation on key technologies and supply chain. Yoon's Government recently expressed hope that Japanese companies would be interested in a $228 billion complex of semiconductors South Korea plans to construct near Seoul by the year 2042.
South Korea is the leading memory chip producer in the world, while Japan provides tools and materials that are essential for chip manufacturing. Washington proposed last year the "Chip 4 Alliance" with two of its allies, Taiwan and South Korea to keep China away from the global semiconductor supply chain.
Fears about Taiwan are on the rise
Seoul, Tokyo and Washington all share a common interest in maintaining peace and stability along the Taiwan Strait.
Analysts are concerned that China could invade Taiwan in a similar way to Russia's invasion of Ukraine. Some experts say that if that were to happen, North Korea could use the opportunity and start a war in the Korean Peninsula.
This would allow the US military to fight on two fronts simultaneously in the area.
Kim Han-kwon is a professor from the Institute of Foreign Affairs and National Security, Seoul. He wrote in a February paper that if a conflict erupts along the Taiwan Strait the United States would demand different cooperation from allies and partners. It sees its bilateral allies with South Korea, and Japan in particular, as important regional strategic assets with regard to the Taiwan Strait.