Future historians may well pick 2019 as a decisive year in the decline of the US and UK as world powers. Of course, the UK started at a much lower level in the international pecking order than the US, but the direction of travel in both cases is the same.

This geopolitical shift comes exactly a century after the Treaty of Versailles, in 1919, when the US and UK were at the peak of their power in determining the fate of nations after the First World War. They self-confidently redrew the map of eastern Europe, the Middle East and Africa according to their own interests and with minimal concern about the effect on others.

Like most political retreats, the present one by the US and UK is masked by patriotic bombast about “Making America Great Again” or launching a post-Brexit “Global Britain”.

In the case of the US, the retreat from hegemony was made manifest this year when Iran carried out a devastating drone and missile attack on Saudi oil facilities in September. Though a blatant act of war against an important US ally, Donald Trump, the US president, swiftly decided that it was not in America’s interests to retaliate. He may be putting maximum economic pressure on Iran, but he made clear he is not going to fight a war against them.

World news in pictures Show all 50 1 /50 World news in pictures World news in pictures 14 September 2020 Japan's Prime Minister Shinzo Abe, Chief Cabinet Secretary Yoshihide Suga, former Defense Minister Shigeru Ishiba and former Foreign Minister Fumio Kishida celebrate after Suga was elected as new head of the ruling party at the Liberal Democratic Party's leadership election in Tokyo Reuters World news in pictures 13 September 2020 A man stands behind a burning barricade during the fifth straight day of protests against police brutality in Bogota AFP via Getty World news in pictures 12 September 2020 Police officers block and detain protesters during an opposition rally to protest the official presidential election results in Minsk, Belarus. Daily protests calling for the authoritarian president's resignation are now in their second month AP World news in pictures 11 September 2020 Members of 'Omnium Cultural' celebrate the 20th 'Festa per la llibertat' ('Fiesta for the freedom') to mark the Day of Catalonia in Barcelona. Omnion Cultural fights for the independence of Catalonia EPA World news in pictures 10 September 2020 The Moria refugee camp, two days after Greece's biggest migrant camp, was destroyed by fire. Thousands of asylum seekers on the island of Lesbos are now homeless AFP via Getty World news in pictures 9 September 2020 Pope Francis takes off his face mask as he arrives by car to hold a limited public audience at the San Damaso courtyard in The Vatican AFP via Getty World news in pictures 8 September 2020 A home is engulfed in flames during the "Creek Fire" in the Tollhouse area of California AFP via Getty World news in pictures 7 September 2020 A couple take photos along a sea wall of the waves brought by Typhoon Haishen in the eastern port city of Sokcho AFP via Getty World news in pictures 6 September 2020 Novak Djokovic and a tournament official tends to a linesperson who was struck with a ball by Djokovic during his match against Pablo Carreno Busta at the US Open USA Today Sports/Reuters World news in pictures 5 September 2020 Protesters confront police at the Shrine of Remembrance in Melbourne, Australia, during an anti-lockdown rally AFP via Getty World news in pictures 4 September 2020 A woman looks on from a rooftop as rescue workers dig through the rubble of a damaged building in Beirut. A search began for possible survivors after a scanner detected a pulse one month after the mega-blast at the adjacent port AFP via Getty World news in pictures 3 September 2020 A full moon next to the Virgen del Panecillo statue in Quito, Ecuador EPA World news in pictures 2 September 2020 A Palestinian woman reacts as Israeli forces demolish her animal shed near Hebron in the Israeli-occupied West Bank Reuters World news in pictures 1 September 2020 Students protest against presidential elections results in Minsk TUT.BY/AFP via Getty World news in pictures 31 August 2020 The pack rides during the 3rd stage of the Tour de France between Nice and Sisteron AFP via Getty World news in pictures 30 August 2020 Law enforcement officers block a street during a rally of opposition supporters protesting against presidential election results in Minsk, Belarus Reuters World news in pictures 29 August 2020 A woman holding a placard reading "Stop Censorship - Yes to the Freedom of Expression" shouts in a megaphone during a protest against the mandatory wearing of face masks in Paris. Masks, which were already compulsory on public transport, in enclosed public spaces, and outdoors in Paris in certain high-congestion areas around tourist sites, were made mandatory outdoors citywide on August 28 to fight the rising coronavirus infections AFP via Getty World news in pictures 28 August 2020 Japanese Prime Minister Shinzo Abe bows to the national flag at the start of a press conference at the prime minister official residence in Tokyo. Abe announced he will resign over health problems, in a bombshell development that kicks off a leadership contest in the world's third-largest economy AFP via Getty World news in pictures 27 August 2020 Residents take cover behind a tree trunk from rubber bullets fired by South African Police Service (SAPS) in Eldorado Park, near Johannesburg, during a protest by community members after a 16-year old boy was reported dead AFP via Getty World news in pictures 26 August 2020 People scatter rose petals on a statue of Mother Teresa marking her 110th birth anniversary in Ahmedabad AFP via Getty World news in pictures 25 August 2020 An aerial view shows beach-goers standing on salt formations in the Dead Sea near Ein Bokeq, Israel Reuters World news in pictures 24 August 2020 Health workers use a fingertip pulse oximeter and check the body temperature of a fisherwoman inside the Dharavi slum during a door-to-door Covid-19 coronavirus screening in Mumbai AFP via Getty World news in pictures 23 August 2020 People carry an idol of the Hindu god Ganesh, the deity of prosperity, to immerse it off the coast of the Arabian sea during the Ganesh Chaturthi festival in Mumbai, India Reuters World news in pictures 22 August 2020 Firefighters watch as flames from the LNU Lightning Complex fires approach a home in Napa County, California AP World news in pictures 21 August 2020 Members of the Israeli security forces arrest a Palestinian demonstrator during a rally to protest against Israel's plan to annex parts of the occupied West Bank AFP via Getty World news in pictures 20 August 2020 A man pushes his bicycle through a deserted road after prohibitory orders were imposed by district officials for a week to contain the spread of the Covid-19 in Kathmandu AFP via Getty World news in pictures 19 August 2020 A car burns while parked at a residence in Vacaville, California. Dozens of fires are burning out of control throughout Northern California as fire resources are spread thin AFP via Getty World news in pictures 18 August 2020 Students use their mobile phones as flashlights at an anti-government rally at Mahidol University in Nakhon Pathom. Thailand has seen near-daily protests in recent weeks by students demanding the resignation of Prime Minister Prayut Chan-O-Cha AFP via Getty World news in pictures 17 August 2020 Members of the Kayapo tribe block the BR163 highway during a protest outside Novo Progresso in Para state, Brazil. Indigenous protesters blocked a major transamazonian highway to protest against the lack of governmental support during the COVID-19 novel coronavirus pandemic and illegal deforestation in and around their territories AFP via Getty World news in pictures 16 August 2020 Lightning forks over the San Francisco-Oakland Bay Bridge as a storm passes over Oakland AP World news in pictures 15 August 2020 Belarus opposition supporters gather near the Pushkinskaya metro station where Alexander Taraikovsky, a 34-year-old protester died on August 10, during their protest rally in central Minsk AFP via Getty World news in pictures 14 August 2020 AlphaTauri's driver Daniil Kvyat takes part in the second practice session at the Circuit de Catalunya in Montmelo near Barcelona ahead of the Spanish F1 Grand Prix AFP via Getty World news in pictures 13 August 2020 Soldiers of the Brazilian Armed Forces during a disinfection of the Christ The Redeemer statue at the Corcovado mountain prior to the opening of the touristic attraction in Rio AFP via Getty World news in pictures 12 August 2020 Young elephant bulls tussle playfully on World Elephant Day at the Amboseli National Park in Kenya AFP via Getty World news in pictures 11 August 2020 French Prime Minister Jean Castex is helped by a member of staff to put a protective suit on prior to his visit at the CHU hospital in Montpellier AFP via Getty World news in pictures 10 August 2020 Locals harvest their potatoes as Mount Sinabung spews volcanic ash in Karo, North Sumatra province, Indonesia Antara Foto/Reuters World news in pictures 9 August 2020 Doves fly over the Peace Statue at Nagasaki Peace Park during the memorial ceremony held for the 75th anniversary of the atomic bombing EPA World news in pictures 8 August 2020 Anti-government protesters try to remove concrete wall that installed by security forces to prevent protesters reaching the Parliament square, during a protest against the political elites and the government after this week's deadly explosion in Beirut AP World news in pictures 7 August 2020 A protester throws a stone towards Israeli forces in the village of Turmus Aya, north of Ramallah in the occupied West Bank, following a march by Palestinians against the building of Israeli settlements AFP via Getty World news in pictures 6 August 2020 A woman yells as soldiers block a road for French President Emmanuel Macron's visit the Gemmayzeh neighborhood. The area in Beirut suffered extensive damage from the explosion at the seaport AP World news in pictures 5 August 2020 Damage at the site of Tuesday's blast in Beirut's port area, Lebanon Reuters World news in pictures 4 August 2020 A large explosion in the Lebanese capital Beirut. The blast, which rattled entire buildings and broke glass, was felt in several parts of the city AFP via Getty World news in pictures 3 August 2020 A general view shows the new road bridge in Genoa, Italy ahead of its official inauguration, after it was rebuilt following its collapse on August 14, 2018 which killed 43 people Reuters World news in pictures 2 August 2020 Empty stall spaces are seen hours before a citywide curfew is introduced in Melbourne, Australia EPA World news in pictures 1 August 2020 People take part in a demonstration by the initiative "Querdenken-711" with the slogan "the end of the pandemic - the day of freedom" to protest against the current measurements to curb the spread of COVID-19 in Berlin, Germany AFP via Getty World news in pictures 31 July 2020 Pilgrims circumambulating around the Kaaba, the holiest shrine in the Grand mosque in Mecca. Muslim pilgrims converged today on Saudi Arabia's Mount Arafat for the climax of this year's hajj, the smallest in modern times and a sharp contrast to the massive crowds of previous years Saudi Ministry of Media/AFP World news in pictures 30 July 2020 The Mars 2020 Perseverance mission lifts off at the Kennedy Space Centre in Florida. The mission is part of the USA's largest moon to Mars exploration. Nasa will attempt to establish a sustained human presence on and around the moon by 2028 through their Artemis programme EPA World news in pictures 29 July 2020 A woman refreshes herself in a outdoor pool in summer temperatures in Ehingen, Germany dpa via AP World news in pictures 28 July 2020 Malaysia's former prime minister Najib Razak speaks to the media after he was found guilty in his corruption trial in Kuala Lumpur AFP via Getty World news in pictures 27 July 2020 North Korean leader Kim Jong Un poses for a photograph after conferring commemorative pistols to leading commanding officers of the armed forces on the 67th anniversary of the "Day of Victory in the Great Fatherland Liberation War". Which marks the signing of the Korean War armistice KCNA via Reuters

In October, it was the turn of the Syrian Kurds to become the next victims of the new American realpolitik when Trump greenlighted a Turkish invasion of northern Syria. Despite having fought heroically and lost 10,000 dead as the US on-the-ground ally in the fight against Isis, the Kurds suffered immediate and predictable ethnic cleansing by Turkey.

The fate of the Saudis and Kurds carried a message about future American actions in the world that was ignored by a largely Trump-bashing media. Dismissing Trump’s foreign policy as crazy and self-serving, establishment critics seldom take on board that, in its crude way, the president’s actions do reflect a changed world order in which the US has lost its old supremacy.

Brutal, shambolic, even treacherous, Trump’s foreign ventures may be, but they often have a core of realism, whether he is dealing with South Korea, Saudi Arabia, Syria or Ukraine. The so-called “grown-ups”, usually military or diplomatic Washington bureaucrats who are protecting their fiefdoms and detest Trump, are often proposing alternative actions in the Middle East or Ukraine that carry a high risk of starting wars that Trump does not want to fight or the US cannot easily win.

None of the Nato leaders gathered in their hotel in Watford this week seemed to have taken on board the lessons of the failed US-led military in the Middle East since Bill Clinton intervened so disastrously in Somalia in 1993 – a war that is still going on.

Trump, likewise, may not know much about the half-dozen militarily conflicts currently raging in the Middle East and North Africa (Mena), but he does see that they are “messy” and “endless” and that America would be well advised to stay out of them.

Significantly, Barack Obama also recognised the ebbing of America’s global hegemony and tried to stall – not always successfully – the enthusiasm for military action inside and outside his administration in Washington. Coming from different directions, both Obama and Trump recognised that the era when the US was the sole superpower that could always expect to get its way is now over.

Trump might easily have gone to war with Iran after a series of Iranian attacks in the Gulf over the course of the summer, culminating in the drone and missile assault on the Saudi oil industry. Sensibly, he decided not to retaliate, demonstrating the new limits on America’s willingness and ability to defend its allies.

The US has lost power, but then it has a lot more to lose than Britain, which saw a much steeper decline in its potential influence in the world in 2019. This had everything to do with impending Brexit as it became clear over the course of the year that the country would indeed be leaving the EU.

It is usually argued that, given the length and complexity of the transition period, Britain will not be really leaving the EU for some time. But the formal act of leaving will have immense impact and immediately diminish British influence in the world.

This is partly because the rest of the world sees Brexit as an act of self-destructive folly, given that 45 per cent of British exports went to EU countries in 2018, compared to only 18 per cent to the US. Suddenly, the country will be without real allies for the first time for over 200 years – historians say the last such moment was during some particularly dire moment during the Napoleonic wars.

Brexit supporters who enthuse about “global Britain” have been wilfully blind to the real balance of power between Britain and the EU as revealed by the withdrawal agreement. It should be obvious that British negotiators failed to get the terms they wanted because their EU counterparts in Brussels held all the high cards.

None of this is going to change: there is something ludicrous about Boris Johnson trumpeting his triumph in reopening the withdrawal agreement when he was only able to do so by accepting the EU’s original proposal of a customs border between Northern Ireland and the rest of the UK and deserting his DUP allies.

At the beginning of 2019, it looked possible that the whole Brexit project might falter or be carried through in a neutered form, but as next week’s general election approaches it looks increasingly inevitable. Britain will be mired in a Brexit crisis of one sort or another for the foreseeable future, trying to establish a new relationship with the EU and the US, both of whom are more powerful and capable of getting their way than the UK.