Japan and China will mark 50 years of diplomatic ties this month with few public celebrations as rising friction over territorial rivalries and disputes over military spending strain ties.

The world’s second and third largest economies are major trading partners and just a few years ago seemed poised for a diplomatic blossoming, with plans for a state visit by Chinese President Xi Jinping.

Since then, relations have deteriorated significantly as Beijing strengthens its military, projects its power regionally and beyond, and takes a harder line in disputed territory.

Chinese missiles are believed to have fallen into Japan’s exclusive economic zone in recent months, and Tokyo has protested what it describes as mounting air and maritime law violations.

Japan also regularly complains about Chinese activity around the disputed Tokyo-controlled Senkaku Islands, which Beijing claims and which Diaoyus calls.

“Chinese ships have been floating in the East China Sea for dozens of days, while an artificial island and base have already been built in the South China Sea,” said Kenichiro Sasae, director of the Japan Institute of International Affairs.

“This leaves us wondering — how far will China’s naval ambitions go?” added Sasae, a former ambassador to Washington and deputy secretary of state.

The war in Ukraine has only deepened the rift, with Japan backing Western allies opposed to the Russian invasion while Beijing avoids criticizing Moscow.

And the conflict has returned attention to whether China might attempt to forcibly reunite Taiwan with the mainland, prompting Japan’s Prime Minister Fumio Kishida to warn that the situation in Ukraine “could be in East Asia tomorrow”.

Beijing and Tokyo normalized relations in a joint communiqué on September 29, 1972, which officially ended their state of war and Japan dropped its recognition of Taiwan.

Economic ties grew rapidly and steadily, but political ties were more unstable, weathering a series of crises including the disputed Senkaku-Diaoyu Islands.

Beijing’s growing power has made Japan “concerned about China,” said Rumi Aoyama, director of the Waseda Institute of Contemporary Chinese Studies.

“Japan views China’s activities in the Senkaku Islands as problematic and includes a ‘core interest,'” she told AFP.

“But the problem is that China doesn’t understand this Japanese perspective. Instead, it tends to see Japan as following only what the US says.”

Tokyo is a long-standing and important US ally, but has expanded its partnerships as a bulwark against Beijing.

It backed a revived “quad” alliance with Australia, India and the United States, and Kishida was Japan’s first leader to attend a NATO summit in June.

“China is gaining power and trust, it’s a trend that cannot be ignored,” said Ken Endo, a professor of international politics at the University of Tokyo and a security expert.

Japan must “declare consistently internationally” that a violent change in the status quo, be it in Ukraine or in Taiwan, is unacceptable.

And he says Tokyo needs a more robust defense capacity, something Kishida and his ruling party have already publicly endorsed, showing that “if you invade us, it’s going to cost a lot.”

Japan is reportedly considering increasing defense spending from the current 1 percent to 2 percent of GDP within five years.

That would mean a sea change in Japan, whose pacifist constitution still limits its military capacity, but a modest increase compared to Beijing’s decades of extra spending.

It could also pose its own dangers and fuel regional tensions if communications with China aren’t carefully managed, Sasae said.

“Every country has contingency plans, including China, but Japan should make it clear that it does not want a military confrontation.”

Japan’s brutal occupation of parts of China before and during World War II remains a sore point, with Beijing accusing Tokyo of failing to atone for its past.

Visits by Japanese officials to the Yasukuni Shrine, which honors war dead – including convicted war criminals – regularly provoke anger from Beijing.

Despite all the tensions, the two countries remain economically intertwined: China is Japan’s largest trading partner and Japan is China’s second largest after the United States.

And reports suggest Tokyo may seek talks between Xi and Kishida, online or in person, in the coming months.

Business connections are “a crucial factor in stopping a relationship from falling,” said Aurelio Insisa, a history professor at the University of Hong Kong and author of a book on Sino-Japanese relations.

But they may not be enough to unfreeze connections.

“Beijing’s behavior in its neighborhood and Tokyo’s perception of it are the two main factors that can change the current dynamic,” Insisa said.

“I wouldn’t bet on an improvement on those two fronts.”