The hundreds of thousands marching were patriots. Not patriots of the flag-waving, chest-beating type, but patriots determined to stop their fellow citizens suffering and a humiliated Britain being torn apart.

“Traitors”, “saboteurs”, “citizens of nowhere”, “Remoaners”... The right has deployed the language of civil war for three years. The insults carried with them the threat that dissenters would be treated as enemies within, but also the promise and the hope that, left to its own devices, Brexit would restore Britain’s greatness.

Now the hope has gone and threats are all that is left. If Nigel Farage remembers his wish to make 23 June a public holiday so future generations could celebrate that glorious moment in 2016 when the British secured their independence from the EU tyranny, no one else does. Boris Johnson and Jacob Rees-Mogg no longer boast of a global Britain enjoying a renaissance. On the far left, the Lexiters who once told us Brexit would give us socialism in one country have fallen silent too.

All that remains on the corpse of the movement that once promised national liberation is a sullen snarl. “The people” voted for Brexit and they must have it – good and hard.

Humiliation was woven into Brexit like a pattern in a fabric. The first aim of English and then British diplomacy since Elizabeth I was to stop the country facing a continent united against her. We face it now, not because Europe is dominated by a Napoleon or Hitler but because “we” have decided to treat our allies as if they were our enemies. No foreign power has reduced Britain to this wretched state. We are a nation that lost a war we declared on ourselves.

If you want to see a snapshot of Britain’s future, look at last week’s picture of EU leaders in a huddle discussing the future of Britain as if they were surgeons discussing a terminally ill patient. Theresa May wasn’t invited to the meeting and her successors won’t be either. Whatever Britain decides, assuming the shock of Brexit does not break up Britain, it will follow the EU nine times out of 10. Soft Brexit, hard Brexit, no-deal Brexit: nothing can free us from our geography and the needs of our economy.

Even as the lights dim around her, May cannot find the courage to challenge the hard right

Mortification is all that unites this shredded country. Nine out of 10 Britons believe the UK’s handling of Brexit is a “national humiliation”, one poll found, but it left a question hanging in the air – how we would react. Nations, like people, respond to humiliation in different ways. They can overcome the disaster that has befallen them and resolve to do better, as West Germany did after 1945, when it went on to create a model democratic republic. Alternatively, humiliation can grind nations down. Or turn them into vindictive states. Revanchism is the default mechanism of much of the world today and it is British exceptionalism at its most arrogant and ignorant to think that it can’t happen here.

The model is not the Germany of 1945 but of 1918 where Hindenburg, Ludendorff and the German general staff explained away their country’s defeat in the First World War with the Dolchstosslegende – the stab-in-the-back myth. The German armies had not been defeated in the field but betrayed by pacifists and socialists in Berlin. General Ludendorff’s biographer recounts how his “eyes lit up and he leapt upon the phrase like a dog on a bone. ‘Stabbed in the back?’ he repeated. ‘Yes, that’s it exactly. We were stabbed in the back.’”

Play Video 3:52 Brexit: May says high time MPs vote for her deal in No 10 statement - video

Eyes have been lighting up ever since, nowhere more so than in the 21st century. Vladimir Putin exploits Russia’s humiliation at the loss of much of its empire in 1991. Recep Tayyip Erdoğan in Turkey and Donald Trump in America feed the fear among devout Muslims and white Americans that they too have been belittled. In what should be the final disgrace of her ignoble premiership, Theresa May, our Thames Valley Trump, our dormitory town Dolchstosslegende, reached for a stab-in-the-back myth of her own when she put all the blame for the Brexit crisis on “parliament [which] has done everything possible to avoid making a choice” and accepted none herself.

All of parliament, mark you. She did not call out the right of the Tory party and the Democratic Unionist party, which have wrecked her administration and give every indication that they will wreck the country, but all MPs and with them Westminster democracy itself. Even as the lights dim around her, May cannot find the courage to challenge the hard right, because, surely, she joined the hard right the moment she put herself on the side of “the people” and against the elected representatives she now characterises as enemies.

To my mind, the descent into authoritarian populism was inevitable. Whether Michael Gove, say, was consciously lying when he said in 2016 that “the day after we vote to leave, we hold all the cards and we can choose the path we want” is an irrelevance. The question has always been how the right would react when it turned out that its promises were false. From June 2016, you only had to pose that question to know the answer. The right would not admit to a mistake. It would imitate Ludendorff and blame the enemies within, even if its flight from responsibility risked destabilising British democracy.

Facebook Twitter Pinterest The Led By Donkeys group has put up billboards repeating Michael Gove’s 2016 claim that “the day after we vote to leave, we hold all the cards and we can choose the path we want”. Photograph: Chris J Ratcliffe/Getty Images

Against today’s conspiracists stand the protesters. As so few others are saying it, I want to end by pointing out how remarkable the upsurge we are witnessing is. Jeremy Corbyn has destroyed Labour as a party of opposition. Yet, without traditional leadership, millions are organising themselves and doing the job of a patriotic opposition for it.

In England, if not Scotland and Wales, the liberal-left has found patriotism an embarrassing subject. How else, however, to describe a mass mobilisation against a deceitful policy that will harm the weakest and diminish us all? If rightists were right, and we truly hated our country, we would not care so much about the bloody mess they have made of it or be so determined to find a better way.

• Nick Cohen is an Observer columnist