Addressing crowds in St. Peter's Square on Sunday, Pope Leo XIV noted the 80th anniversary of the end of World War II and -- echoing his predecessor Pope Francis -- declared, "Never again war."

Leo urged an end to the ongoing wars in Ukraine and the Middle East. "I carry in my heart the suffering of the beloved Ukrainian people," he said. "Let us do everything possible to reach a genuine, just and lasting peace as soon as possible. May all prisoners be freed and children be able to return to their families."

"I am deeply saddened by what is happening in the Gaza Strip," he added. "Let the fire cease immediately. Let humanitarian aid be provided to the exhausted civilian population and let all hostages be freed."

"On the other hand, I welcomed with satisfaction the announcement of the ceasefire between India and Pakistan, and I hope that through the upcoming negotiations we can soon reach a lasting agreement," Leo continued.

-ABC News' Phoebe Natanson

Pope Leo XIV addressed crowds at the Vatican on Sunday, asking those gathered to pray for the priesthood.

The new pope spoke to the crowd to give the Regina Caeli prayer. Police estimated that there were around 100,000 people in St. Peter's Square to watch Leo's address.

-ABC News’ Phoebe Natanson

On his way back to the Vatican, Leo stopped by the Basilica of Saint Mary Major, and prayed before the tomb of Pope Francis, according to the Vatican press office.

He also prayed at the icon of the Virgin, Salus Populi Romani, that is the same icon Pope Francis used to visit before and after every foreign visit and in other occasions.

-ABC News' Phoebe Natanson

In an instant, Cardinal Robert Prevost became the most powerful and influential American Catholic when he was selected to be pope and renamed Pope Leo XIV on May 8.

But with the United States' standing in the world on edge with President Donald Trump in office, experts say many will be watching the first American to lead the Catholic Church to see how he walks the tightrope between Western politics and his papal duties.

Vatican experts told ABC News that Leo must thread that needle effortlessly, with a focus on leading from a global perspective.

"I suspect he will be scrupulous and careful to avoid the thought that he is an American and not a Christian view," the Rev. Stephen Spahn, an assistant teaching professor of theology at Loyola University Maryland, told ABC News. "He is going to be a bridge builder and build relationships with world leaders broadly."

At the same time, experts predicted Leo will not hesitate to speak out on U.S. matters from his seat when needed.

Spahn said cardinals have always come to their decisions knowing that the man who becomes pontiff will have to work within the geopolitical environment in pushing forward the Catholic Church's mission.

"It's definitely going to trail him. How could it not?" he said of the pope's Americanism. "But the cardinals have said they chose him without any regard to his nationality."

-ABC News' Ivan Pereira

Pope Leo's past statements suggest he may take different positions on some social issues than his predecessor Pope Francis did.

In 2012, he expressed concern about Western media promoting what he called "beliefs and practices that are at odds with the gospel," including same-sex relationships, according to the New York Times. As a bishop in Peru from 2015 through 2023, he opposed teaching gender studies in schools, stating that "gender ideology is confusing, because it seeks to create genders that don't exist."

That appears to mark a departure from Francis's more welcoming approach to LGBTQ+ issues. Francis famously asked "Who am I to judge?" when discussing gay clerics, and made headlines with his decision to allow same-sex couple blessings.

In other areas, like women serving in leadership roles in the Catholic Church, Leo has taken a more progressive stance.

In a 2023 interview with Vatican Media, Leo XIV highlighted his experience with having women in church leadership, particularly discussing the three women appointed to help select bishops -- a reform he oversaw under Francis.

"Their opinion introduces another perspective and becomes an important contribution to the process," he told Vatican Media, emphasizing that their roles represent "real, genuine, and meaningful participation."

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