Experts are already warning it’s unlikely much will be achieved when the heads of the world’s 20 leading economies meet for the G20 summit in Hamburg, Germany, this week.

With Brexit, North Korean aggression, the Qatar crisis, allegations of Russian interference in the US election and the ongoing fight against Islamic State, world leaders have a lot to discuss. Yet these issues and others have caused several diplomatic rifts.

Additionally, US President Donald Trump pushing an unashamedly ‘America First’ message, the summit’s official priorities – including things like climate change and refugee flows – read like a repudiation of the White House agenda.

“These challenges will certainly not be mastered by countries plotting a lone course, or with isolationism and protectionism,” German chancellor Angela Merkel writes in the official statement of priorities for the summit.

But with a number of highly anticipated side meetings on the agenda, including the much anticipated first face-to-face meeting between the US President and his Russian counterpart, this year’s summit may be the most contentious yet.

Key G20 meetings

Donald Trump and Vladimir Putin

This is the one we’ve all been waiting for. The two leaders have been famously complimentary towards each other; this will be their first face-to-face meeting. Rather than a ‘pull-aside’, official bilateral talks have been arranged. “There’s no specific agenda. It’s really going to be whatever the President wants to talk about,” HR McMaster told CNN recently.

Back in the US, Democrats will demand Mr Trump raise alleged Russian interference in the 2016 election, an issue currently being investigated by a special prosecutor.

Donald Trump and everyone else

German Chancellor Angela Merkel is expected to focus the talks on climate change, particularly given Mr Trump’s recent decision to pull the US out of the Paris climate accord. Mr Trump has signalled a desire to renegotiate the deal – Ms Merkel, who has said Germany will step up to help “save the world”, was among those who immediately ruled that out.

France’s new president, the centrist Emmanuel Macron, is essentially the anti-Trump. He’s already made no secret of his desire to rattle the President, including the infamous ‘death grip‘ handshake and cheeky tweets mocking Mr Trump’s campaign slogan.

Prime Minister Malcolm Turnbull, meanwhile, grabbed world headlines after mocking Mr Trump at an ‘off-the-record’ parliamentary ball. This will be their first meeting since.

Mr Turnbull will reportedly push Mr Trump to compel American tech companies to assist anti-terrorism investigations by helping authorities to unlock encrypted communications devices.

Vladimir Putin and Angela Merkel

Following Brexit and the election of Mr Trump, Ms Merkel has emerged as the de facto leader of the liberal, outward-looking West. While she is not expected to ‘shirtfront’ Mr Putin (to quote Tony Abbott), Ms Merkel has said Germany would take “decisive measures” against possible Russian interference in the country’s elections later this year. Mr Putin recently admitted relations between the two countries were “problematic”, amid disagreements over Crimea and Syria.

Xi Jinping and Moon Jae-in

Elected after a corruption scandal ended his predecessor’s career, South Korea’s new president has now been tasked with keeping millions safe from the threat of nuclear disaster. With North Korea launching its first “successful” intercontinental missile this week, Mr Moon says he will seek reinforced co-operation from the rest of the world. Key to this will be an increased effort from China, he says. While he is seeking a meeting with Xi Jinping, China reportedly called off trilateral talks with South Korea and Japan slated for the end of the month, citing the US-funded THAAD missile defence system.

Angela Merkel and Xi Jinping

With Mr Trump ratcheting up pressure for China to handle North Korea, threatening a trade war over steel and recent tensions in the South China Sea, observers say the Chinese President will be eager to affirm Beijing’s relationship with Europe’s largest economy.

Mr Xi called for the two nations to strengthen their bond in a guest column in a German newspaper this week. Both countries should both take responsibility for world “peace, stability and prosperity”, he wrote.

Yet things are complicated by China’s human rights record and, perhaps more crucially, the fact Germany has not hesitated in doling out the criticism on this issue.