The world cannot afford to fail at this a third time

At what? Setting up an international system to prevent catastrophic wars between major powers that inflict massive civilian casualties and destruction of property and cultural assets.

The first time was the Concert of Europe after the Napoleonic Wars. The second was the League of Nations after World War I. And the third was the United Nations and related international institutions after World War II.

Without drastic life support, the third is in a death spiral, epitomised by the statement from US President Donald Trump saying: "I don't need international law." That statement came after US forces invaded Venezuela and kidnapped its president.

Some history will illustrate the ghastly ramifications of what Trump has done and said in the past fortnight.

In a way, the Napoleonic Wars (1803-1815) was the first world war, affecting multiple major nations and fought across vast areas. It was characterised by huge cost to civilians in life, limb and property.

After the peace was hammered out at the Congress of Vienna, the UK, Austria, Prussia, Russia, and France joined to form the Concert of Europe. It was unlike earlier peace treaties which just divided the spoils and cost among the victors and vanquished.

Rather, it joined all the major powers into an agreement to engage in diplomatic and collective action to prevent large-scale wars. For the first time there was a sense that modern war had no victors because they were all-out wars.

With a couple of small exceptions, it brought nearly a century of peace among the great powers and there was no war in which all major powers joined in. Diplomacy triumphed until nationalism, jingoism, and autocratic leaders over-shadowed any warnings about the horror and cost of war and the big powers entered World War I in 1914 - 22 million died, more than half were civilians.

Again, the great powers vowed "never again". The Great War (as it was then called) would be the war to end all wars.

The US led the charge. President Woodrow Wilson wanted more than a treaty to end the war. He wanted more than just the diplomacy of the Concert of Europe. He sought an international organisation of all nations dedicated to peace and the avoidance of war and to ending the main causes of conflict by promoting self-determination and an end to imperialism and colonialism.

Wilson, a genuine peace-seeker was awarded the Nobel Peace Prize, something Trump should never get.

But the League failed. World War II ensued. After it the major powers tried for a third time to set up a global institutional framework to avoid great-power war. The United Nations was set up with an anti-imperialist anti-colonial element, just like the League of Nations.

Two other elements were added, largely under US leadership - a rules-based financial and trading system and the trial of the individuals who caused the waging of war.

The trying of the war leaders of Germany and Japan for war crimes was to criminalise war - to make it abnormal - not normal. The US renamed its Department of War in 1948, to the Department of Defense. Britain renamed its War Office in 1964. Last year Trump changed the name back to the Department of War.

Napoleon was not tried or held personally responsible. Neither was the Kaiser. World War II was different. Waging an aggressive war became the "supreme international crime" because the architects of war are personally responsible for all the death and destruction that follows.

The UN Charter made it unlawful for a nation to wage war except in self-defence. It was not an excuse for an individual country to invade another country to unseat a tyrant. Better to tolerate a local tyrant (for his own people to unseat) than to threaten world peace with unilateral aggression.

Based on that, I believe Trump's action in ordering the invasion of Venezuela was a war crime. That is why his rejection of international law is so threatening to world peace.

Trump's actions against Venezuela are the sort of things the UN was set up to condemn, declare unlawful, and prosecute the perpetrators.

Trump's stance now poses a series of questions for US allies, like Australia. Do we continue to ally ourselves with a nation whose leader behaves in a lawless way and threatens further lawless aggressive behaviour in the hope that it will self-correct in three years?

The soothing noises that respective leaders of Australia and the US have made whenever there was a change of government in either country in the past that the alliance is greater than the complexion of the politics of either government, now have no foundation.

Or do we say that we want to keep the protection of the mighty US military even if its Commander in Chief is a liar, unreliable, and a transactional kleptocrat who I believe is guilty of war crimes?

What store do we put on the words of the ANZUS treaty that the three nations "reaffirm our faith in the purposes and principles of the Charter of the United Nations and their desire to live in peace with all peoples and all Governments".

The ANZUS and NATO treaties are there for Australia and the co-signatories to stand up to aggression, not to ally ourselves with it.

With Trump and his America First policy the world is becoming more like that predicted by George Orwell in his 1948 novel Nineteen Eighty-Four in which three totalitarian superstates - Oceania, Eurasia and Eastasia - are engaged in perpetual war and control their populations through fear, scarcity, and propaganda.

The history is important because it tells us about the cost of rejecting diplomacy, collective action, international institutions, and international law, however flawed or imperfect.

When the pre-eminent world power rejects and undermines that system, as Trump did this month, the unthinkable comes closer. People start talking about warfare, military strategy, weapons systems, and military spending as if a war can be "won".

With modern arsenals, there can be no winners. If we mess up the third attempt at constructing a system to avoid major-power war, we may not get a fourth chance.