The vote on the security bills threatens to further strain ties between Japan and its neighbors, which have shown signs of improvement in recent months. The U.S., which has ensured Japan’s defense since the conflict, is seeking a greater security role for its ally as China becomes a naval power.

Japanese Prime Minister Shinzo Abe brought the legislation to a vote just weeks before he’s expected to make a statement to mark the 70th anniversary of the war’s end. Both China and South Korea have called on Abe to apologize for war-time atrocities committed during occupation by Imperial Japan.

Arms Race

Passage of the security bills “could provide more ammunition to nationalism in both China and Japan, which could hurt the still fragile bilateral ties,” said Wang Xinsheng, a professor of history who specializes in Japan and East Asian politics at Peking University. “The new bills could also refresh neighbors’ memories of Japan’s wartime aggression and spark an arms race in the region.”

Japan’s ties with China and South Korea have deteriorated as territorial disputes flared and new leaders adopted more assertive foreign policies.

The value of trade between South Korea and Japan fell 6 percent in 2014 from the previous year. Japan’s trade with China was stagnant last year after sliding 6 percent slide in 2013.

Narushige Michishita, a professor of security studies at the National Graduate Institute for Policy Studies in Tokyo, said the legislative change was necessary to move Japan away from isolationism. “It’s a significant responsible decision on the part of Japanese leaders to go ahead and start sharing some more burdens,” he said.

‘Reasonable Step’

Abe’s efforts to court his regional counterparts in recent months have appeared to bear fruit, despite his continued pursuit of the security legislation.

Chinese President Xi Jinping has met Abe twice since November. China’s top diplomat, State Councilor Yang Jiechi, said after a meeting with Abe aide Shotaro Yachi in Beijing on Thursday that the two nations agreed to hold high-level political dialogue.

Last month, Abe and South Korean President Park Geun Hye called for an improvement in ties over the next half-century.

“Japan’s discussions on defense policy should be made transparently, adhering to the pacifist constitution and supporting regional peace,” Yoo Chang Ho, a spokesman for South Korea’s foreign ministry, said in a press briefing Thursday in Seoul. “We solemnly urge the Japanese government to learn from history, insist on peaceful development, and respect the safety concerns of all Asian countries.”

‘Nightmare Scenario’

If Japan’s upper house refuses to take up the security bills, a second vote in the lower house would pass them into law. The vote drew harsh rebuke from China’s state-run media, with the official Xinhua News Agency publishing a commentary saying that “a nightmare scenario has come a step closer for Japanese people and neighboring nations.”

The bills’ passage would “tarnish the reputation of a nation that has earned international respect for its pacifist Constitution over a period of nearly seven decades,” the commentary said, citing opposition to the legislation in Japan. “For countries that fell victim to Japan’s aggression, the chills sent by the bills are even more acute.”