ROME — Pope Francis defended “modern multilateral diplomacy” and international institutions against “the resurgence of nationalistic tendencies” in an address at the Vatican on Monday.

Francis did not cite specific countries in his speech, delivered to diplomats at the Holy See, but he appeared to be lamenting the mix of jingoism and isolationism that has emerged in the United States and in European nations where populist governments have risen to power.

Noting that the League of Nations, established after World War I, had failed to head off another war largely because countries were not willing to work together, Francis raised the specter of fresh violence.

“The same attitudes are presently threatening the stability of the major international organizations,” he said, urging Europeans in particular to remain united in the face of “temptation to erect new curtains.”