China and Russia now appear to be on such great terms, one wonders how long it can last. If the history of relationships between the two after China’s emergence under Communist rule in 1949 is any guide, they won’t stay best friends forever — and maybe not for long.

“No matter how the international landscape may change, China will stay committed to advancing China-Russia comprehensive strategic partnership of coordination for the new era,” China’s foreign ministry spokesman, Wang Wenbin, says, but the Sino-Soviet dispute of the late 1950s and early 1960s suggests a different outcome.

The issue then ostensibly was that of ideological differences after the death of Joseph Stalin as leader of the Soviet Union in 1953 while China under Mao was still waging the Korean War against America and South Korea. The full extent of the rift became apparent after Stalin’s successor, Nikita Khruschev, initiated de-Stalinization and denounced the “cult of personality” that had dominated the Soviet Union under Communist rule.

Now, the contest is between the strongest ruling figure in Moscow since Stalin and the strongest leader in Beijing since Mao.

President Putin does not control nearly all the territory of the former Soviet Union, which claimed satellites from eastern Europe to central Asia, but he clearly dreams of recovering the power of Moscow beginning with Ukraine. President Xi is extending China’s reach from the South Pacific to the Middle East.

Will the two march together into that glorious future?

“China is ready to work with Russia to build on past achievements, enrich the comprehensive strategic partnership of coordination for the new era, bring more benefits to the two peoples, and make greater contribution to human progress,” Mr. Wang says.

That’s a grandiose program that avoids offering Mr. Putin a firm commitment to anything. Beyond formal statements, future relations rely on a degree of trust that’s never existed between China and Russia any more than it did between the Soviet Union and Germany when they signed their “non-aggression pact” in 1939 — nearly two years before Hitler ordered the German invasion of the Soviet Union.

If China and Russia are not going to invade each other’s territory, they still have to maintain smooth relations along their 2,500-mile frontier extending across Siberia. Cross-border relations have not always been smooth.

“Xi is old enough to remember when Sino-Russian relations were fraught and the risk of a Sino-Soviet nuclear exchange was real,” a China expert at Brookings in Washington, Ryan Hass, writes. “The two countries fought a border conflict in 1969, when Xi turned 16.” For years, he writes, “the Soviet Union maintained a massive military presence along the Sino-Soviet border, deploying up to 36 divisions.”

For China, enduring peace with Russia is central to focusing on Aukus, the Australia-U.K.-U.S. alliance that China fears almost as much as Russia hates NATO for its support of Ukraine.

“China views the United States as the principal obstacle to its rise,” Mr. Hass says. “Having to focus on securing its land border with Russia would divert resources and attention from China’s maritime periphery, where Xi feels the most acute threats.”

Just as important, Mr. Xi needs Mr. Putin’s unstinting support for his ambitions all around Asia. It’s for that reason he’s invited Mr. Putin to Beijing for China’s third belt-and-road forum, in which heads of state talk about economic cooperation. The prime beneficiary, of course, is China, expanding trade through its “new Silk Road” through Pakistan and central Asia to the Middle East and Europe.

Mr. Putin has been to two previous belt-and-road forums and is likely to go again. “Neither Beijing nor Moscow can deal with the United States and its partners on its own,” Mr. Hass observes. “They both would rather stand together to deal with external pressure than face it alone.”

Under the circumstances, Mr. Xi’s proposal for peace is a device for keeping Moscow firmly on his side while he faces the line that Washington has drawn from Korea to Taiwan and the South China Sea.

“After reaching consensus with Russia,” Global Times, published by China’s party newspaper, People’s Daily, says, “China will engage with other major powers with key influence … and will keep in touch with Ukraine, and also might seek suggestions from other key neutral parties.”

In the great bargaining game, Ukraine is a chip that Mr. Xi is playing for all he can extract from Moscow against Washington.