Climb into my time machine and come fly with me two years into the future. Here we are, November 2018, with celebrations of the centenary of the end of the First World War in full swing. And we find ourselves part of the grand coalition that has just declared war on China.

Throughout the noughties and beyond, the itch we couldn’t stop scratching was the Muslim world. Our war was the war on terror, we were told, and when that “crusade” collided head-on with the Arab Spring, the result was Syria. Seven years on, the bloody stalemate grinds on. Nobody can win. Nobody is prepared to yield an inch. It’s Flanders Field all over again.

But meanwhile, at the beginning of 2016, a real old-fashioned war was boiling up in the South China Sea, only we were not paying attention. And now the British government is talking about conscription – a century after the heroes came home. It’s so funny it hurts.

It was when politicians started talking about Thucydides that we should have pricked up our ears. President Xi Jinping started it in a speech in Seattle in September 2015 – only to flatly deny the ancient Greek historian any relevance to the growing rivalry between the US and China. “We want to deepen mutual understanding with the US on each other’s strategic orientation and development path,” he said. “There is no such thing as the Thucydides Trap in the world. But should major countries time and time again make the mistake of strategic miscalculation, they might create such traps for themselves.”

The “Thucydides Trap” explained the origins of the Peloponnesian War. “It was the rise of Athens, and the fear that this inspired in Sparta,” Thucydides wrote with classical crispness, “that made war inevitable.” And that ancient conflict set the tone for 2,400 years of organised butchery, with the First and Second World Wars as the most recent specimens. Until now.

The rise of Germany and the threat that Germany’s ever-expanding navy posed to Britain set the scene for the Thucydides Trap of the First World War. The nature of the danger was spelled out in 1907 in a note by a British Foreign Office official called Eyre Crowe. “Germany would clearly build as powerful a navy as she can afford,” Crowe wrote, and that navy would pose a fatal challenge to the British Empire whatever Germany’s protestations to the contrary. As Crowe noted, dry as sandpaper, “Ambitious designs…are not as a rule openly proclaimed, and even the profession of unlimited and universal political benevolence [is] not conclusive evidence” against “unpublished intentions.” Seven years later these two brotherly powers were duly fighting to the death.

The growth in tensions between the US and China has been uncannily similar. In Seattle, Mr Xi pooh-poohed the dead Greek but in the years before that speech, China had converted thousands of merchant ships for military use, developed a “carrier killer” missile specifically designed to sink American aircraft carriers, tested hypersonic glide vehicles said to be capable of striking the US with nuclear warheads, and stealthy submarines armed with ballistic missiles. In 2015, despite the general slowdown of the economy, China increased its military budget by 10 per cent, and one Chinese general warned that once the build-up was complete, “No enemy will dare to bully us.”

That is the assertion that is now to be tested. February 2016 marked the point of no return. Five years before, as its economic power ballooned, Beijing submitted a diplomatic note to the UN Secretary-General asserting its sovereignty over islands in the South China Sea – batting aside rival claims to coastal zones by Vietnam, Taiwan, the Phillipines, Malaysia and Brunei. Instead China claimed the lot. Regional hegemony was in China’s national DNA. Historically all its petty neighbours had tried to ensure peace by paying annual tribute. In the modern world, tribute took the form of unresisting obedience.

But then Barack Obama came to power in Washington and he and Secretary of State Hillary Clinton chose to execute a “pivot to Asia”, to bolster the morale of those Asian small fry while making it clear that China would not have it all its own way. And as has happened in international summitry since the time of Pericles, sweet talk, fraternal visitations and hearty dinners proceeded in tandem with steely military build-ups on both sides. The Chinese version is sketched above. The US military budget continued to dwarf those of all its possible rivals put together, and America carried out huge war games in the Pacific to practice fighting China. Then in February 2016, after American incursions into the South China Sea, the US accused China of installing surface-to-air missiles on Woody Island, one of the uninhabited atolls on which tension had focused. China retorted that it was US air and naval patrols in the region that had “escalated tensions.” And there was to be no looking back.

Is this, then, the dawn of the nuclear Doomsday we have lived in fear of since Hiroshima? In a study some years back, Harvard professor Graham Allison analysed 16 cases of the Thucydides Trap during the past 500 years, noting that 12 of them resulted in war. The good news – the glass half-full – was that four of them didn’t. Three of those, notably the Soviet-US Cold War, post-date the Second World War. The nuclear threat was part of the reason. But where war was avoided, Professor Allison wrote: “It required huge, painful adjustments in attitudes and actions on the part not just of the challenger but the challenged.”