Former President Barack Obama on Tuesday offered a sharp rebuke of his successor's worldview.

Obama delivered the 2018 Nelson Mandela Annual Lecture in South Africa, slamming "strongman politics" and the rejection of intellectualism he feels is permeating today's political culture.

Obama did not once say President Donald Trump's name during the address, but his words represented a biting critique of the current president's political philosophy.

Obama concluded his speech by encouraging young people to stay politically active and have faith in democracy despite how "slow" and "frustrating" it can be at times.

Former President Barack Obama on Tuesday offered a sharp rebuke of his successor's worldview as he delivered the 2018 Nelson Mandela Annual Lecture in South Africa, slamming "strongman politics" and the rejection of intellectualism he feels is permeating today's political culture.

Obama did not once say President Donald Trump's name during the address, held one day before what would've been Mandela's 100th birthday. But his target was clear as he offered a biting critique of the current president's political philosophy.

The former president used the speech as an opportunity to outline what he views as troubling trends in the political arena.

"Strongman politics are ascendant suddenly," Obama said. "Whereby elections and some pretense of democracy are maintained, the form of it. But those in power seek to undermine every institution or norm that gives democracy meaning."

'The free press is under attack'

As Trump on Tuesday again used Twitter to denounce "Fake News," a phrase he typically employs in response to negative coverage of his actions or rhetoric, Obama said that "the free press is under attack."

Obama also urged people to reject xenophobia and "rabid nationalism," warning that history shows countries that embrace "doctrines of tribal, racial, or religious superiority" eventually "find themselves consumed by civil war or external war."

"You can be proud of your heritage without denigrating those of a different heritage," Obama added.

Obama's speech came after Trump's high-profile visit to Europe, which Trump claimed was losing its "culture" because of immigration policies.

"These people who are so intent on putting people down and puffing themselves up, they're small-hearted," Obama said. "There's something they're just afraid of."

'You have to believe in facts'

In addition to warning against the dangers of excessive nationalism, the former president expressed concern over the apparent rejection of objective truth among leaders.

"You have to believe in facts. Without facts, there's no basis for cooperation," Obama said, adding: "Unfortunately, too much of politics today seems to reject the very concept of objective truth. People just make stuff up."

An analysis from The Washington Post in May found that Trump had made at least 3,001 false or misleading claims so far as president.

Obama concluded his speech by encouraging young people to stay politically active and to have faith in democracy despite how "slow" and "frustrating" it can be at times.

"Keep believing. Keep marching. Keep building. Keep raising your voice. Every generation has the opportunity to remake the world," Obama said. "Mandela said, 'Young people are capable, when aroused, of bringing down the towers of oppression and raising the banners of freedom.' Now is a good time to be aroused."