Former Vice President Mike Pence said Tuesday that signs of diminished U.S. support for longtime allies have left him worried about conflict and strife akin to one of the deadliest eras in world history.

“I think we’re living in a very perilous time where America needs to be strong, we need to be ready, we need to stand with our allies, and we need to make it clear to enemies of freedom that — as President Kennedy said — we will bear any burden, pay any price to ensure the survival of liberty,” Pence said. “We stay strong, we stay unwavering, make it clear to people that we’re going to defend our interests and our allies in the world, and we got a shot at a peaceful future. Failing that, I think the second half of the 21st century could look a whole lot more like the first half of the 20th century.”

Pence spoke at the Kennedy School during an event hosted by the Institute of Politics and moderated by Archon Fung, director of the Ash Center for Democratic Governance and Innovation. It came months after Pence was awarded the Profile in Courage Award by the John F. Kennedy Library Foundation in Boston for his role certifying the 2020 election results as rioters surrounded the U.S. Capitol.

The U.S. is irreplaceable on the world stage because there’s no other allied nation that other countries will follow, Pence said, linking his own recent run for president to his sense that Donald Trump and others in the GOP were stepping back from global leadership.

“What drew me into my brief but memorable campaign back in 2023 was that I saw my old running mate and many in our party departing from those core ideals and principles,” Pence said. “If America isn’t leading the free world, the free world is not being led. There is no B team, no backup country that steps into that gap.”

Specifically, Pence said that the U.S. should help put Ukraine in a better position to defeat Russia. Otherwise, he said, the risk of a third world war will rise.

“Anyone who thinks yielding to a rapacious dictator avoids World War III needs to study World War II,” Pence said. “In my judgment, Vladimir Putin won’t stop until he’s stopped.”

Pence didn’t break with the current administration completely. He cited his support for lower taxes. He cast doubt on global warming prescriptions and insisted that climate solutions come from free market, rather than regulatory, approaches. He also voiced support for the Supreme Court’s 2024 decision overturning the Chevron doctrine, which had given regulators a powerful voice in interpreting and filling in gaps in laws passed by Congress.

Pence said that his Christian faith has been a powerful motivator for him in public life and that he believes that democracy requires that the people share a common moral order. He also affirmed the First Amendment’s religious freedom clauses.

He traced to his faith his belief that civility in politics is not just a courtesy to opponents, but an important feature that allows people to meet across differences.

“Democracy depends on heavy doses of civility,” he said. “When we’re civil with one another, even when we disagree, we have the opportunity to find common cause, not compromising principles or core values, but actually finding ways to work together to advance the country.”

Fung thanked Pence for his actions on Jan. 6, 2021, when Pence refused to bow to pressure from President Trump and the protesters invading the Capitol as Congress gathered to certify Joe Biden’s election victory. He also asked the former vice president about his faith in the durability of U.S. institutions.

Recalling Jan. 6, Pence said, “Many around the world were watching and I think they saw the resilience of our institutions and the strength of our institutions.”

He added: “I have confidence in the days ahead that Republicans and Democrats will hew to those roots and to that duty.”