In the summer of 2015, America caught a glimpse of how its future could unfold. The US military conducted a routine exercise in the south that triggered a cascade of conspiracy theories, particularly in Texas. Some believed the manoeuvre was the precursor to a Chinese invasion; others thought it would coincide with a massive asteroid strike. The exercise, called Jade Helm 15, stood for “homeland eradication of local militants”, according to one of the right’s dark fantasy sites. Greg Abbot, Texas’s Republican governor, took these ravings seriously. He ensured that the 1,200 federal troops were closely monitored by the armed Texas National Guard. In that bizarre episode, which took place a year before Donald Trump became the Republican nominee for president, we see the germs of an American break-up.

As with any warning of impending civil war, the very mention of another American one sounds impossibly alarmist — like persistent warnings from chief Vitalstatistix in the Asterix comic series that the sky was about to fall on Gaulish heads. America’s dissolution has often been mispredicted.

Yet a clutch of recent books make an alarmingly persuasive case that the warning lights are flashing redder than at any point since 1861. The French philosopher Voltaire once said: “Those who can make you believe absurdities can make you commit atrocities.” As the University of California’s Barbara Walter shows in her bracing manual, How Civil Wars Start, US democracy today is checking all the wrong boxes.