China and Russia are openly displaying their strengthened military ties as a counterweight to the U.S. These activities will not only heighten tensions between the two sides, but also deeply affect the security environment of Northeast Asia. These developments should raise alarms.

Chinese forces recently participated in Russian-hosted large-scale military exercises for the second year in a row. China sent 1,600 service members, along with fixed-wing aircraft and helicopters, according to Chinese media. The drills in southwestern Russia ran for six days, ending Sept. 21.

China pledged at the Communist Party congress two years ago to have military modernization basically completed by 2035. It had earlier set a goal of a world-class military by the middle of this century.

Chinese military expansionism, symbolized by outposts in the South China Sea, has awakened strong misgivings in the U.S. and contributed to the increased pressure on Beijing. Standing behind the escalation of the Sino-American trade war, which has incorporated the battle for technological supremacy, is the hard line of President Xi Jinping’s government.

China released its first defense white paper in four years this summer. The document singles out the “comprehensive strategic partnership” with Moscow and mentions Chinese participation in Russia’s Vostok strategic exercise in Siberia around last fall.

Xi’s administration is considering collaborating with Russia to develop technology with possible military applications. At a mid-September summit in St. Petersburg, Chinese Premier Li Keqiang and his Russian counterpart agreed to expand cooperation in such high-tech fields as artificial intelligence and robotics.

Russia’s wealth of knowledge in military tech, when combined with China’s aptitude for technology development, would pose a significant threat to the U.S. and risk ratcheting up tensions further. All sides should practice restraint.

But the honeymoon between Beijing and Moscow is not certain to last. China is busy expanding its influence in Russia’s backyard of Central Asia. There, complex gamesmanship is afoot. Russia remains wary of a China that has become an economic power it cannot compete with.

These developments have an enormous impact on Japanese national security. Russian and Chinese military aircraft have conducted their first joint patrols over the Sea of Japan and the East China Sea. Tokyo needs to fully analyze the facts behind this major shift, then develop measures to counter the threat while working closely with its ally Washington.