History never repeats itself, but it sure does rhyme, it has been said.
Now an internationally respected historian is warning that today's world bears a number of striking similarities with the build-up to the First World War.
The newly mechanised armies of the early 20th century produced unprecedented slaughter on the battlefields of the "war to end all wars" after a spark lit in the Balkans with the assassination of the Austro-Hungarian Empire's Archduke Franz Ferdinand.
A nuclear arms race that would be likely to start if Iran developed a bomb "would make for a very dangerous world indeed, which could lead to a recreation of the kind of tinderbox that exploded in the Balkans 100 years ago – only this time with mushroom clouds," she writes in an essay for the Brookings Institution, a leading US think-tank.
"While history does not repeat itself precisely, the Middle East today bears a worrying resemblance to the Balkans then," she says. "A similar mix of toxic nationalisms threatens to draw in outside powers as the US, Turkey, Russia, and Iran look to protect their interests and clients."
Professor MacMillan highlights a string of other parallels between today and a century ago. Modern-day Islamist terrorists mirror the revolutionary communists and anarchists who carried out a string of assassinations in the name of a philosophy that sanctioned murder to achieve their vision of a better world.
And in 1914, Germany was a rising force that sought to challenge the pre-eminent power of the time, the UK. Today, the growing power of China is perceived as a threat by some in the US.
Transitions from one world power to another are always seen as dangerous times. In the late 1920s, the US drew up plans for a war with the British Empire that would have seen the invasion of Canada, partly because it was assumed conflict would break out as America took over as the world's main superpower.
Professor MacMillan, whose book The War That Ended Peace was published last year, said right-wing and nationalist sentiments were rising across the world and had also been a factor before the First World War
In China and Japan, patriotic passions have been inflamed by the dispute over a string of islands in the East China Sea, known as the Senkakus in Japan and Diaoyus in China.
"Increased Chinese military spending and the build-up of its naval capacity suggest to many American strategists that China intends to challenge the US as a Pacific power, and we are now seeing an arms race between the two countries in that region," she writes in her essay.
"The Wall Street Journal has authoritative reports that the Pentagon is preparing war plans against China – just in case."
The US has a mutual self-defence treaty with Japan and in 2012 it specifically confirmed that this covered the Senkaku Islands. In November, China set up an "air defence" zone over the islands and a few days later two American B-52 bombers flew over the islands in defiance of Beijing.
"It is tempting – and sobering –to compare today's relationship between China and the US with that between Germany and England a century ago," Professor MacMillan writes.
She points to the growing disquiet in the US over Chinese investment in America while "the Chinese complain that the US treats them as a second-rate power".
Another similarity highlighted by the historian is the belief that a full-scale war between the major powers is unthinkable after such a prolonged period of peace.
"Now, as then, the march of globalisation has lulled us into a false sense of safety," she says. "The 100th anniversary of 1914 should make us reflect anew on our vulnerability to human error, sudden catastrophes, and sheer accident.
"Instead of muddling along from one crisis to another, now is the time to think again about those dreadful lessons of a century ago in the hope that our leaders, with our encouragement, will think about how they can work together to build a stable international order."