During his state visit to Russia in June, Chinese President Xi Jinping effusively hailed Russian President Vladimir Putin as his "best friend and colleague." Putin, not to be outdone, replied by affirming his personal respect for Xi and suggested that Sino-Russian relations have progressed not only to an "unprecedentedly high level" in recent years, but are now increasingly based on a "truly comprehensive partnership and strategic interaction."

But whatever Putin means by "strategic interaction," and despite the undeniable progress in Sino-Russian relations over the past decade, it is easy to fall into the trap of exaggerating what some fear as the emerging Sino-Russian "alliance" in world politics.

Notwithstanding the Xi-Putin friendship and the growing congruence of both countries' interests in undermining the U.S.-led international order, relations between Russia and China remain at the core as brittle and prone to mutual suspicion and distrust as they have in the past.

It was, after all, only 50 years ago this year when the two Eurasian giants nearly stumbled into a cataclysmic war following a series of unprovoked Chinese attacks on Soviet troops garrisoned along the then-contested river boundaries in Russia's Far East. Although Moscow stayed its hand from an all-out military assault on China, the border clashes of 1969 continue to shape historical memories and military thinking in Russia to this day.

Such territorial jostling along the vast Eurasian landmass, which the 1969 events highlight, in fact, has defined Russo-Chinese relations historically, and will continue to do so in the future.

And therein lies the existential rub, especially for Russia: from a Russian strategic planner's perspective, a China with nearly a billion-and-half people not only dwarfs Russia in population, national power and economic might, but, more worryingly, has become a near military equal prone to intimidate and throw its weight around its periphery at will. Witness, for example, Beijing's swift and brazen conquest of the South China Sea, the unrelenting pushing and probing into Vietnamese, Philippine and Japanese maritime spaces and, in the West, frequent incursions, standoffs and aggressive territorial claims against India.

None of these acts of Chinese belligerence will have escaped the notice of Russian planners who, despite the paradox of Russia's shared strategic interests with China to counter America's continuing dominance in world affairs, are nonetheless bound to view China's rapid and inexorable rise into the front rank of global powers with acute consternation.

Short-term harmony

But despite any apprehension that Moscow may quietly harbor, Russo-Chinese relations in the short term – over the next four or five years – are likely to remain largely in harmony, mainly because Putin's carefully tended relationship with Xi enables him, among other things, to maintain the pretense of Russia as a great power, attract Chinese investment and, more generally, project an image of himself as a world-class statesman.

And Xi, although leading an immeasurably more powerful country than Russia except in offensive nuclear firepower, tactfully grants Putin the appearance and status of an equal through elaborately choreographed summit meetings, the bestowing of high level state and friendship awards, and personal respect, in order to secure at least tacit deference by Moscow to a Sino-centric Eurasian geopolitical order currently being planned in Beijing.

Yet, beyond the apparent bonhomie and geopolitical dalliance between Xi and Putin, the historic and atavistic tensions deeply rooted between the Slavic and Han civilizations represented by Russia and China are bound to emerge again, and most probably in a violent form, in the next decade.

In fact, signs already abound of Russian nervousness as China relentlessly pushes its Silk Road initiatives, coercive economic practices and diplomatic blandishments deep into the entire former Soviet space in Central Asia. Although the Chinese have so far refrained from asserting strategic-security rights in the geopolitical arc along Russia's southern periphery, it can only be a matter of time before some hyper-nationalist general in Beijing does so, and the Russians can be betted upon to react with unrestrained fury.

But what will certainly drive Russia to a defensive war with China before the next decade is out is the growing probability of Chinese territorial encroachment into Russia's sparsely populated Far Eastern region bordering the Pacific. The Russian territories north of the Amur and east of the Ussuri rivers in eastern Central Asia, which currently demarcate the agreed geopolitical boundaries between the two countries, are lands historically and insistently claimed by China. Chinese military maps even show these areas as Chinese territories.

These territorial claims, combined with sheer population disparities – over 130 million people live in three Chinese provinces bordering Russia's Far East, where population is estimated at less than 8 million – and the need to secure long term access to living space and natural resources, almost preordains Beijing to sooner or later demand revisions to what it calls "unequal" border treaties with Czarist Russia dating back to mid-19th century.

Possible scenario

Although the Russians are bound to resist any Chinese push, it is not inconceivable that China at some point will demand access or land lease rights to parts of Russia's Far East, or failing that, for the Chinese army will simply march across the border into Vladivostok, Russia's only warm water access to the Pacific, to stamp China's historic claim and rights to the region.

It is not clear at this juncture how Russia and China can step back from a conflict in the coming decade. But as China appears unlikely to relinquish its expansive territorial claims against its neighbors in the near future, including Russia, the onus for deterring China from seizing Russian territories will fall upon Putin, or his successors, in the 2020s.

But whether China can be deterred remains to be seen. If the current Xi-Putin bromance fails to tamp down China's geostrategic ambitions across Eurasia, expect a war between the two nuclear-armed states in the 2020s.

* Consultant on defense and international security based in London