In his final speech to the United Nations, President Barack Obama warned against denying globalization and promoting isolationism, calling it "self-defeating," according to the NPR. Obama also said:

"Today a nation ringed by walls would only imprison itself."

While Obama did not directly mention Donald Trump, this is undoubtedly an indirect jab at the Republican presidential candidate's protectionist economic policy, immigration plans, and seeming disregard for NATO, a coalition of North American and European nations assembled after World War II to ensure military cooperation.

Trump has previously said:

"We don't have a country if we don't have borders. We will build a wall. It will be a great wall. It will do what it's supposed to do: keep illegal immigrants out. [...] We need a border. We need a wall. [...] We have to stop the inflow of illegals coming into our country."

In July, Trump raised alarm over comments in which he set conditions for upholding the NATO alliance, which calls for automatically defending NATO allies if they are attacked, according to The New York Times.

The Times reports:

"Asked about Russia’s threatening activities, which have unnerved the small Baltic States that are among the more recent entrants into NATO, Mr. Trump said that if Russia attacked them, he would decide whether to come to their aid only after reviewing if those nations have 'fulfilled their obligations to us.'

'If they fulfill their obligations to us,' he added, 'the answer is yes.'"

As the Times notes, "Mr. Trump’s statement appeared to be the first time that a major candidate for president had suggested conditioning the United States’ defense of its major allies. It was consistent, however, with his previous threat to withdraw American forces from Europe and Asia if those allies fail to pay more for American protection."

Trump's posture on international affairs contrasts sharply with President Obama, who has favored coordinating with NATO allies in the protracted war against terrorism, and pushed for the controversial Trans Pacific Partnership, which critics say would worsen problems associated with global economic markets.

In his address to the U.N., Obama acknowledged global trade and free markets has fostered income inequality all over the world, saying "we do have to acknowledge that the existing path to global integration requires a course-correction," NPR reported. He also said, "Too often those trumpeting globalization have ignored inequality."

In another veiled dig at Trump, Obama said "real problems" with globalization have been ignored, which has given rise to "aggressive nationalism" and "crude populism...often from the hard right," reports CNN.