Brexiteers like Boris Johnson must realise that past British successes were based on creating alliances, not breaking them up

The British only stood alone during the centuries when they had miscalculated the political wind direction, or had been left with absolutely no alternative

What will be Britain’s standing in the world compared to other nation states after Brexit? Sane analysis has been overwhelmed by vituperative debate as we get closer to the day of the great rupture.

Boris Johnson claimed in his resignation speech that after a full-throttle Brexit, Britain will be in a good position to become “one of the great independent actors” on the world stage. He feared only a failure in the necessary will-power and self-confidence “to believe in this country and what it can do”.

But what can this country really do? How far will greater independence outside the EU be real rather than nominal? Will strength of will in pursuit of self-determination make much difference when we will always be holding a weaker hand of cards than our neighbours?

This imbalance of forces is highlighted every day in the Brexit negotiations, and there is no reason why this should change in our favour after we leave.

Supporters of Brexit discount such realpolitik, saying that they are inspired – and seek to emulate – a past in which Britain as a fully independent state won victories against the odds. Critics often deride this approach as self-indulgent nostalgia, but there are real lessons to be learned from past British experience.

The problem is that Brexiteers, when they take a serious view of British history that is not coloured by Shakespeare’s plays or Errol Flynn movies, have never shown much understanding of the roots of Britain’s successes.

The British only stood alone during the centuries when they had miscalculated the political wind direction, or had been left with absolutely no alternative. At the heart of British strategy was the drive to join or create alliances with other countries powerful enough to overcome any enemy.

It was this formula that put Britain on the winning side in the Napoleonic Wars, the First World War and the Second: the three great conflicts that shaped the contemporary world.

Against Napoleon, it was the combination of Britain with Russia, Prussia and the Habsburg Empire that produced the victory for which the British traditionally claimed exaggerated credit. In the 1914-18 war, the British priority was to bring about US intervention, and the same was true in 1939-45.

Britain only stood heroically alone during a relatively short period between the fall of France in 1940 and Hitler’s invasion of the Soviet Union in the summer of 1941, followed later in the year by his declaration of war on the US after Pearl Harbour.

Churchill’s record as a military leader was dubious in both wars – remember Gallipoli and Norway. His greater and more valuable skill was to foster and maintain a grand alliance against Germany which was bound to win in the end. The centrality of these alliances tends to be masked by unwavering focus on Dunkirk, the Battle of Britain and the triumphs of the British codebreakers.

British pre-eminence was based on defence by the Royal Navy, which prevented invasion, and the patient construction of a war-winning coalition. The last time Britain fought a major conflict without such an alliance was the American war of independence, which concluded with disappointing results for our side.

Exaggerated presumptions of national superiority are scarcely a monopoly of the Brexiteers, or even of the British, but the referendum has made them peculiarly destructive. What is interpreted as unfair bullying by the EU, or unnecessary timidity on the part of Theresa May, is simply a reflection of our inferior – and their superior – strength.

Johnson suggested that Britain might do well to emulate Trump’s negotiating style of laying down the law and threatening to walk away. But he crucially missed the point that such bravado is the perquisite of the strong, and weak countries do not dare to bluff because that bluff is likely to be called.

It would be a caricature of the Brexiteers’ mentality to imagine that they believe that what worked well at Crecy, Blenheim and El Alamein has much to do with what goes on at present. But this mythology does create a national mood that makes it difficult for the English – the same is no longer true of Britain as a whole – to carry out any great political enterprise.

Brexit is only the latest in a series of British ventures this millennium in which political class has miscalculated what we could accomplish. The process was already evident when Britain was engaged in wars in Iraq, Afghanistan and Libya, and failed to achieve its ends in all three of them.

There is nothing secret about what happened. The Chilcot Report, for instance, lucidly explained in great detail how the British government did not know what it was getting into in Iraq and ended up, after all its efforts, signing a humiliating truce agreement with a local Shia militia in Basra.

Britain was repeatedly caught by surprise by events, tumbling out of Iraq into even bloodier skirmishing in Helmand province in Afghanistan. In Libya, it should have been perfectly obvious that if Gaddafi fell, there was nobody but predatory militias to replace him, and much the same was true in opposing Bashar al-Assad in Syria.

At some point, the British political, diplomatic and military establishment seems to have lost its touch or capacity to learn from experience.

The difficulty people have in picturing life after Brexit is that what are essentially political issues are framed in economic terms, so anxiety and hope are directed far too much towards the future economic consequences of Brexit. This diverts attention from the fact that the political disaster is already with us and visible for all to see.

Britain has been generally more united than its rivals and opponents over the last three centuries, but Brexit has provoked a degree of disunity not seen since the 17th century. It is absurd for the Brexiteers to keep saying that “the nation” decided to leave the EU in the referendum, and act as if this were so, because nothing is clearer than that the nation is split down the middle.

And the very definition of that nation – is it the United Kingdom or England? – is in doubt, since Scotland voted to remain, as did a majority in Northern Ireland. The Brexiteers scarcely seem to notice that they have reopened the Ulster Question, which bedevilled British politics from Gladstone’s efforts to pass a Home Rule Bill in the 1880s to the Good Friday Agreement in 1998.

In the eyes of the rest of the world, a country that once seemed to possess the secret of stability has become permanently self-absorbed in its own divisions. Johnson’s puerile bombast and jingoism has its uses because it neatly sums up what is not likely to happen: “A great Brexit” he claimed “will unite this party, unite this House and unite this nation.”

But nothing is less likely to happen. Brexit is exacerbating all other grievances and divisions. These will be worse after Brexit than before. Britain is already weaker than at any time since the end of the Stuart monarchy.