Seoul, South Korea(CNN) In uniting Western democracies against Russia's invasion of Ukraine, United States President Joe Biden managed something his critics thought was impossible.
Before Moscow's unprovoked war, European nations were split over issues ranging from Russian energy pipelines to Brexit and -- with lingering resentments dating back to Trump-era trade disputes and the Iraq war -- some even appeared to be rethinking their relationship with Washington.
Yet just three months on and -- as shown by Finland and Sweden's eagerness to join NATO -- Biden can say with some justification that the West is "stronger and more united than it's ever been."
Now, as he flies into Asia for his first trip as President, Biden faces a similarly daunting task in uniting two Asian democracies: South Korea and Japan.
The two countries are Biden's strongest allies in the region -- together they are home to more than 80,000 American troops -- and the US sees both as vital to building a coalition of like-minded countries to combat two threats potentially even more threatening to world peace than Russia's invasion: the rise of China and North Korea's nuclear program.
The stakes could hardly be any higher. US Secretary of State Anthony Blinken recently referred to China's rise as "the biggest geopolitical test of the 21st century" -- and that was after the Russian invasion.
Meanwhile, North Korea has carried out fifteen missile launches so far this year and despite Pyongyang declaring a "severe national emergency" last week due to a Covid-19 outbreak, Washington believes its seventh nuclear test and further intercontinental ballistic missile tests may be imminent -- and possibly timed to coincide with Biden's trip.
Hence Washington's desire to see Japan and South Korea unite.
The problem for Biden? While both appear keen to get closer to Washington, when it comes to each other the two countries just do not get along. They have a historically bitter and fractious relationship that is rooted in Japan's colonization of South Korea from 1910 to 1945, and that was inflamed by Japan's use of sex slaves in wartime brothels -- victims now referred to euphemistically as "comfort women." What's more, they remain locked in a 70-year dispute over the sovereignty of a group of islets in the Sea of Japan, which Korea calls the East Sea.
These differences are no historical curiosities, but live disputes. At one of the most recent attempts at trilateral talks, in November 2021, a joint press conference was derailed when the Japanese vice foreign minister objected to a South Korean police chief's visit to the islets -- known as Dokdo by South Korea but Takeshima by Japan. Lawsuits brought against Japanese companies over their use of forced wartime labor remain unresolved. Recent years have seen increasing differences on security and economic issues.
Evans Revere, a former US diplomat who has been in and out of government over the past 50 years, with stints on both the Korea and Japan desks, has watched the sourness of the relationship undermine alliances over a period of decades.
"If Tokyo and Seoul are not talking with each other actively, if they're not cooperating with each other, it's very difficult for the US to carry out not only its obligations to them but its strategy of dealing with China, dealing with North Korea," he said.
Thankfully for Biden, Revere says he is feeling more hopeful now than he has for a very long time.
Both South Korea's President Yoon Suk Yeol and Japan's Prime Minister Fumio Kishida are newly installed leaders and both have shown signs of hawkish stances on North Korea and China, as well as an eagerness for stronger military ties with the US.
Japan's still influential former leader Shinzo Abe has called on Tokyo to consider hosting US nuclear weapons, while South Korea's Yoon has suggested he would consider joining the Quad -- the US-led loose security grouping that includes Japan, India and Australia and will hold a summit meeting that Biden will attend towards the end of his trip.
Crucially, the two new leaders have also shown signs of putting the past behind them. Yoon offered an olive branch to Japan last month by sending a delegation to Tokyo ahead of his inauguration as part of his plan -- outlined in a campaign speech -- for South Korea to make a "fresh start" as a "global pivotal state."
His team hand delivered a letter from Yoon to Kishida and the move was reciprocated this month when Japan sent Foreign Minister Yoshimasa Hayashi to Yoon's inauguration with a letter in reply.
After receiving the letter, Kishida said strategic cooperation between Japan, the US and South Korea was needed "more than ever, given that the rules-based international order is under threat."
But even if the countries' leaders see the benefit in putting the past behind them, they will be keen to avoid alienating voters who may not be as forgiving.
Professor Kohtaro Ito, a senior research fellow at The Canon Institute for Global studies, said that while Yoon had shown signs of a changing approach -- choosing a foreign minister in Park Jin who could speak both English and Japanese and is popular in the Japanese parliament -- any breakthrough during Biden's trip is unlikely.
That's because both must still navigate looming local elections -- South Korea has local polls in June and Japan has upper house elections in July -- and neither leader will want to alienate nationalist voters less disposed to letting bygones be bygones.
This is hardly the first time the two countries have tried to overcome their differences. In 1965 they signed a treaty that normalized relations and was supposed to settle some of the most controversial issues -- including that of the "comfort women."
But South Korea was a military dictatorship at the time and many Koreans have never accepted the treaty. For some, subsequent apologies and deals from Japanese prime ministers have still fallen short of what they deem sufficient reparations.
Choi Eunmi, a research fellow in Japanese Studies at the Asan Institute for Policy Studies, said that a Japan-South Korea alliance would be vital for Biden's hopes to build a coalition, but felt his visit would do little to settle these problems.
"It is too sensitive and too controversial and there is no room for America to resolve the issues," she said.
There are the voters to think of.
Revere highlights "the nationalism that often drives the perceptions of this relationship and historical issues in both capitals" as a spoiling factor and the role of the South Korean courts that -- through their rulings on wartime disputes -- "could bring any effort at reconciliation crashing down."
For decades, families of Korean forced labor victims have been fighting for compensation through the courts, targeting the Japanese companies directly.
It's an issue that has infuriated Tokyo, which believes things were resolved with the 1965 treaty, and an issue Yoon can hardly address without being accused of interfering in the independence of the judiciary.
Yoon also starts his single five-year term with the lowest approval ratings of any incoming President and has to work with an opposition-dominated parliament.
In Japan, the older and generally more conservative generation largely supports a tougher approach to South Korea and Kishida will be well aware of that, said Ito, who added that the older generation voted in far greater numbers than the younger one.
Biden, though, is likely to have one clear message that could cut through any lingering political doubts harbored by Kishida or Yoon: the importance of alliances and cooperation, as demonstrated by Russia's invasion of Ukraine.
"The President of the US has been absolutely instrumental in mobilizing the international community, mobilizing NATO allies and others to support Ukraine in its moment of need," Revere said.
"What better statement about the importance and value of the utility of alliances than what is happening right now."