"With the rise of populist movements and questions about the future of European integration, my visit to Greece - the birthplace of democracy and an inspiration for America's founders - will be a chance to reaffirm the enduring values of democratic governance, diversity and tolerance that help keep us strong", he said. Obama must now convince foreign governments and populations that the future isn't as bleak as he once predicted.

Air Force One touched down midmorning in Athens after an overnight flight from Washington amid severe security measures that shut down major roads and banned public gatherings and demonstrations in swathes of central Athens and a southern suburb near a seaside luxury hotel where Obama was expected to stay. "And so one of the messages I will be able to deliver is his commitment to North Atlantic Treaty Organisation and the transatlantic alliance". "The U.S. president has repeatedly stated he wants to solve this huge issue before he leaves office".

Since the election, however, Obama has promised to ensure a smooth and peaceful transition of power, largely backing off his criticism that Trump is unfit to serve as US commander-in-chief.

Obama said distrust of elites and governing institutions had fed success in the USA election for Senator Bernie Sanders, who challenged Hillary Clinton in a drawn-out Democratic primary contest, and for Trump, a former reality TV star who bested the former secretary of state in the US presidential race. "And they're vital for the world".

Ukip acting leader Nigel Farage, an architect of the Brexit vote, was an adviser to Mr Trump and has said the two victories share a common revolutionary thread.

Obama arrived in the Greek capital earlier Tuesday.

The lesson of the election, he said, is that "we have to deal with issues like inequality". And he's promised to scrap key multilateral accords that formed large parts of Obama's foreign agenda, including a deal reached in Paris past year to reduce global carbon emissions and the pact with Iran to curtail its nuclear ambitions.

American voters may have decided they "just need to shake things up", he said.

"People are less certain of their national identities or their place in the world".

Obama is on a week-long, three-stop foreign swing that has taken new urgency following Trump's election. Greece has been the main gateway into Europe for refugees and other migrants from Syria, Iraq and Afghanistan. He said leaders should heed lessons from results in the U.S. and in Britain, which in June voted to exit the European Union.

But he'll also provide a rebuttal against arguments for a more walled-off continent, insisting Europe works better as a joint power.

United States president Barack Obama has said fears of globalisation and suspicions of government institutions and elites powered both the UK's vote to exit the European Union and Donald Trump's election as the next U.S. president. "We have to deal with economic dislocation".

"President Obama must use his visit to shine the spotlight not only on abysmal conditions for the tens of thousands of refugees stranded in Greece, but also on the failure of world leaders to adequately address the wider global refugee crisis", Amnesty International's Europe director, John Dalhuisen, said in a statement.

Trump did win, and Obama still isn't sure what he would have done differently.

He'll also meet with the leaders of the United Kingdom, France and Italy, and "signal our solidarity with our closest allies and express our support for a strong, integrated, and united Europe".