That moral is also the lesson drawn from appeasement of the Nazis during the 1930s, including in the highly praised new study by Tim Bouverie, Appeasing Hitler (Bodley Head, April 2019).

Do not underestimate the resolve of the enemy, its capacity to take risks, bear costs, dissemble and deceive. When confronted by lethal adversaries, do not kid yourself that acts of aggression are just one-offs. Do not count on treaties being honoured. The word of your enemy is not to be trusted. Do not expect disputes to be settled without resort to force.

If resolution is the critical variable, we should focus on the quality and integrity of our own leaders.

Appeasement teaches us not to encourage adversaries to underestimate our determination and commitment.

Other lessons flow from that premise. Do not ignore looming threats; fight early and on your own terms; do not listen to plausible enemies; be prepared to bring on and live with sacrifices; educate public opinion into a matching resolve. As Winston Churchill reminded those of little faith, courage is the cardinal virtue because it guarantees all the others.

Courage begins at home. As Shakespeare's Brutus was warned centuries ago, the fault "lies not in the stars, but in ourselves". In the time of Brexit and Donald Trump, democracies might examine again one darker side of appeasement, the reasons voters tolerate ignorantly blind, delusionary leaders. The 1930s offer grim cautionary tales for every generation.

Britain's performance was so sordidly suicidal that we can easily persuade ourselves that we would have done better. Throughout Hitler's early challenges, Sir this and Lord that still dressed for dinner, rode to hounds, relied on servants, despised foreigners and condescended to Jews.

Moreover, not enough British luminaries bothered to read Hitler's Mein Kampf, surely the biggest target ever set out by an opposition leader.

Of successive British foreign secretaries, wits remarked that the only foreigners one understood were the ancient Greeks, while the other minister was said to resemble the last in a long line of maiden aunts. The British ambassador to Germany wrote a dispatch on pages torn from a detective novel, and loftily rebuked the German foreign minister for uttering the adjective "damned" in conversation.

The population of Czechoslovakia was being damned at the time.

Compared with their leaders, a few more alibis may be allowed for the general public. In Britain and France alike, ordinary folk were exhausted by the Depression, hagridden by memories of trenches, gas and shelling, preoccupied by concern that "the bomber will always get through" or bedevilled by the demographic impact of their huge losses in the war just gone (which led in France to the hollow years, "les annees creuses").

What excuse do democracies now offer for any vestiges of 1930s-style displays of fecklessness or listlessness?

In Australia, we might wonder when Senate Republicans will recognise the ignominy attached to blind allegiance to Trump. We might muse about when the British might give their country a second chance with another referendum on Brexit.

Nonetheless, even for a country as isolated and insulated as Australia, the appeasement decade provides a few bracing lessons. God willing, our predicaments will never be anywhere near as atrocious as those of the 1930s, but there are still counsels of prudence which we might heed.

The first is obvious. Insistence on tax breaks and reliance on sugar hits do not guarantee security. Defence requires dollars. Britain's chronic underspending on defence cost the country authority, credibility and, eventually, lives.

Second, do not deprecate putative allies. Through the 1930s, the British did not miss an opportunity to disdain and disparage Soviet Russia, even when the Russians might have helped forestall Hitler (over Czechoslovakia) or avert a war (before their non-aggression pact in 1939).

Less excusably still, the British leadership seemed determined to hold the United States at a rather arch, snobbish, arm's length. In each case, they certainly underestimated the other's resolve.

Third, maintain enough bandwidth. Thousands of lives were lost from not paying sufficient advance attention to Japanese motives and intentions.

Everyone, Australia especially, suffered from London's myopic reliance on one easily besieged seaport (Singapore) and a few easily sunk warships.

Fourth, do not rely on other countries to do the heavy lifting. During the 1930s, France and Britain engaged in a pointless, gutless game of "after you, Alphonse", each waiting for the other to take an initiative or to demonstrate commitment. Neither did.

Fifth, face facts. Intellectual Maginot lines are no more likely to be effective than France's actual line proved in 1940. To borrow two Churchill phrases from the time, there is no sense in a government "decided only to be undecided, resolved to be irresolute".

Sixth, do not permit a government to hide behind public opinion, despite the legitimacy of the fears and phobias which the public might believe.

I met a British veteran on Juno beach on the 50^th anniversary of D-Day. He had been told that German defences had been pulverised, and he should wade ashore, stroll along to a paddock, then make himself a cup of tea.

By nightfall, not only were those illusions dispelled. All his mates were dead, and he was left wondering about the workings of life, death and fate - without any tea to be had.

He might well have asked why appeasement had led him to that Normandy beach.