MY grandfather was a pacifist in the First World War. He was also an elder of the Kirk, and was thrown out for his opposition to conscription. That would be inconceivable today, and is perhaps a measure of just how far militarism has been expunged from public consciousness. We simply can’t imagine millions of men going willingly – and most did – to be slaughtered on an industrial scale in the trenches, and with the Church urging them on. The passions that drove war fever have long lain dormant.

But that doesn’t mean they couldn’t be revived, or that global war is now impossible, and couldn’t happen. The Great War, which ended 100 years ago today, was supposed to be “the war to end all wars”. If you’d told the people of Britain, shattered from the loss of one million souls, that they would be back at war with the same enemy in just 21 years’ time, they would probably have punched you in the face. They did a lot of that in those violent old days.

Global war seems inconceivable because my generation, the post-war baby boomers, have lived almost our entire lives without having to face the prospect of being called up to serve in a global conflict. This is something for which we should be immensely grateful, of course. My father lived through two world wars, fascism, Stalinism and the Great Depression. We’ve had it easy – perhaps too easy. We take peace for granted.

The Cold War, which ended in 1991 with the collapse of the Soviet Union, was an almost entirely theoretical conflict, fought by military planners and war gamers, who were trying to prevent an actual war happening. They nearly failed at least twice: during the 1962 Cuban Missile Crisis, and in the 1983 Operation Able Archer panic, when the Soviet Union’s aged leader, Yuri Andropov, mistook a Nato exercise as preparations for a nuclear first strike.

If you want to learn just how close we came to World War Three 35 years ago, it’s worth reading Ben Macintyre’s recently published biography of the defector Oleg Gordievsky, The Spy And The Traitor. Then a leading KGB agent, Gordievsky briefed a sceptical MI6 that the Kremlin, believing that the West was planning a first nuclear strike, was busy preparing to get there first. As a result, Margaret Thatcher persuaded Ronald Reagan to reduce the perceived threat to the Soviet Union. Gordievsky later played a significant role in persuading both leaders that Western provocations, including the Star Wars anti-ballistic missile shield, and medium-range nuclear missiles in Europe, were creating dangerous instability. This was what CND and the Western peace movement had been arguing for years.

But that all seems in the past, like Aldermaston marches. Surely the threat of nuclear war has gone with the passing of the Cold War? Unfortunately, it hasn’t – the threat of nuclear conflict is arguably greater today than at any time since Able Archer, and the fact that this is not part of public consciousness is good reason to be worried about it. Some of the very treaties that prevented the Cold War going hot, like the 1987 Intermediate Nuclear Forces Treaty, have recently been scrapped by America, claiming Russian violations.

There are signs that world leaders have either forgotten how to actively prevent war happening – or no longer care. Bellicose demi-militarists like Donald Trump and Vladimir Putin utter rhetoric that echoes the reckless nationalism of the last century. They are not National Socialists, don’t wear jackboots and aren’t promoting a master race. But these “hard men” are dismantling the rules-based international order that developed in the latter stages of the Cold War, based on human rights, arms control and economic co-operation. Economic nationalism is back, with America launching trade wars against most of the Asian continent, from Iran to China.

Indeed, rivalry with China, which was peripheral to the Cold War, is today probably the biggest threat to world peace, the greatest “known unknown”. Last year, Steve Bannon, then Donald Trump’s chief strategist, predicted war with China “within the next 10 years ”. He wasn’t alone. Barack Obama also foresaw problems in the South China Sea and in 2009 famously “pivoted” US military strategy towards southeast Asia. He developed the AirSea Battle doctrine, ASB, designed to equip the US to fight a war with China. Not surprisingly, China saw this as something of a threat.

As the author of Silk Roads, Professor Peter Frankopan, has been arguing, there has been a structural shift in the geopolitical balance of the world in the last 25 years or so. In some ways, this mirrors the shifting imperial rivalries that developed in the years leading up to World War One. China, the most populous country on the planet, is scheduled to overtake America as the world’s biggest economy in the next decade or so and is causing much consternation in the White House. It’s an incredible achievement for a country that was one of the world’s poorest until the late 20th century. But tectonic changes in the global structure of economic power rarely take place without earthquakes.

America dominated most of the world after the defeat of the Nazis and Japan in 1945, then became the sole superpower after 1991. But history didn’t end there. Now we have a new superpower emerging in China and a defeated superpower, Russia, trying to re-establish its military credibility, in Syria and Europe. There is a crisis of confidence in the Pax Americana, a rise in military adventurism elsewhere, coupled with widespread economic uncertainty in Western countries following the financial crash.

As Frankopan points out: “The great winners of globalisation have been the global poor in Asia; the great losers have been the middle classes in countries like America”. Discontent among the winners-who-are-becoming-losers could play a number of ways, but it already appears to be fuelling an increase in international tensions. The behaviour of Donald Trump, and his willingness to engage in confrontation, is a sign of American weakness, rather than strength. But it’s a dangerous game and, as the US midterms show, it may not be a temporary aberration.

On the other side, no-one should be under any illusions about the Chinese regime, which remains a dictatorship, suppressing human rights, locking up dissidents and denying free speech. It also has a strong militaristic posture and the largest army on the planet, the People’s Liberation Army. The leader of the Chinese Communist Party, president Xi Jinping, has just altered the constitution to end presidential term limits – which effectively makes him leader for life. Elderly dictators do not make good rulers, and they have a habit of resorting to force to get their way.

I’m not saying that we are heading towards World War Three, but the relatively stable, binary world of the Cold War has passed, leaving a more confusing and fractious geopolitical landscape. The rise of nationalism in the West has taken everyone by surprise, and shown how quickly public attitudes can change when livelihoods are at stake. However, the First World War also came as a complete surprise and, when it started, everyone thought it would be short-lived. The lesson is always to expect the unexpected; and, as we remember the dead, that the price of peace is eternal vigilance.