Barack Obama has told an audience in Berlin that prosperous nations could not "hide behind a wall" to shield themselves from the turmoil and poverty afflicting other countries.
Speaking in a panel discussion on democracy with German Chancellor Angela Merkel in front of 70,000 people at a spot where the Berlin wall once stood, Obama spent 90 minutes talking about international and US issues without once mentioning his successor Donald Trump.
But in what appeared to be a reference to Trump's vow to build a wall along the border with Mexico to keep out illegal immigrants and drugs, Obama said the world was shrinking due to globalisation and technology.
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It was not possible to stay isolated from troubles abroad, he said.
"If there are disruptions in these countries, if there is bad governance, if there is war or if there is poverty, in this new world that we live in we can't isolate ourselves," Obama said.
"We can't hide behind a wall."
Obama, who was making his first speech in Europe since leaving the White House, also warned against taking peace and prosperity for granted.
"The world is at a crossroads," said Obama, speaking in front of the Brandenburg Gate.
The widening inequality gap inside nations as well as between nations was a major concern, he said.
At the same time, "the world has never been wealthier, more healthy and never been better educated."
"If we can sustain that progress, then I'm very optimistic about our future. My job now is to help them take it to the next step."
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Obama said he had spent the last four months "trying to catch up with my sleep" and spending more time with his family.
"I'm very proud of the work I did as president," he said to cheers, adding he was especially proud of health care reform.
"My hope was to get 100 per cent of people health care. We didn't quite achieve that but we were able to get 20 million people health care who didn't have it before.
"Certainly I have some regrets that we weren't able to get everyone health care.
"Now some of the progress we made is imperiled because a significant debate is taking place in the United States," he added, again avoiding direct mention of Trump, who is attempting to dismantle the so-called Obamacare program.
