President Obama used his final address to the United Nations General Assembly to implicitly argue against the immigration and trade policies of Republican nominee Donald Trump.

In a speech Tuesday, Obama criticized politicians on the far left and far right who push “a crude populism” that “seeks to restore what they believe was a better, simpler age free of outside contamination.”

Then he appeared to reference Trump’s biggest proposal, a wall along the Mexican border.

“I believe that the acceleration of travel and technology and telecommunications, together with a global economy that depends on a global supply chain, makes it self-defeating ultimately for those who seek to reverse this progress,” he said. “Today, a nation ringed by walls would only imprison itself.”

He also appeared to critique Trump’s proposal to raise tariffs on imports from China and Mexico, a move many economists say would lead to a trade war.

“If we start resorting to trade wars and market-distorting subsidies, beggar-thy-neighbor policies and overreliance on natural resources instead of innovation, these approaches will make us poorer collectively and they are more likely to lead to conflict,” Obama said.

Instead, Obama outlined a broad agenda of strengthening labor unions, spending on early childhood education and infrastructure and increasing foreign aid, among other things.