ROME — The new Chicago-raised Pope Leo XIV faces an immediate challenge in his native country: taming the brawling U.S. tribe of Catholics, riven by political divisions that have thwarted the will of his predecessors.

Pope Leo XIV will formally take up his role as leader of the global Catholic Church on Sunday, with a Mass in St. Peter's Square that will draw tens of thousands of well-wishers, including dozens of world leaders and European royalty.