"War drags people into a spiral of violence which then proves difficult to control; it tears down what generations have labored to build up, and it sets the scene for even greater injustices and conflicts," he said in a written message to a world summit of religious leaders.
"War is never a necessity, nor is it inevitable. Another way can always be found: the way of dialogue, encounter and the sincere search for truth," he wrote.
The pope's message was presented Sept. 7 to people taking part in the International Meeting of People and Religions, organized by the Rome-based lay Community of Sant'Egidio and hosted by the Diocese of Antwerp, Belgium.
More than 300 leaders representing the world's religions participated in the global summit, which was being held Sept. 7-9. Its aim was to create an international alliance of religions dedicated to peace and dialogue and to countering fundamentalist ideologies and violence.
In his written message read to participants Sept. 7, the pope said this year's 100th anniversary of the start of World War I "can teach us that war is never a satisfactory means of redressing injustice and achieving balanced solutions to political and social discord."
Citing the wartime pope, Pope Benedict XV, Pope Francis said, "All war is ultimately 'senseless slaughter'" that ruins lives and poisons relationships.
"We cannot remain passive in the face of so much suffering," he said.
The pope urged the world's religious leaders to cooperate in "healing wounds, resolving conflicts and pursuing peace."
Among those speaking at the summit in Antwerp was Ali Abtahi Sayyed Mohammad, a former vice president of Iran and current president of Iran's Institute for Interreligious Dialogue.
"Radicalism is the product of an alliance between tyrants and ignorant followers," Abtahi said Sept. 8.
All conflicts based on presumably religious motives have shown that political leaders are the ones fomenting the violence, trying to convince "the devout that they are the only authentic religious group in the world and that the other religions are deviant and false."
True religious believers, he said, "are those who understand the essence of religion" and are "always against war and the hostility that religious radicalism spreads in the world."
Abtahi said the radical religious groups, al-Qaida and fighters for the Islamic State, developed because of support from the West, "especially from the United States," in order to carry out Western interests.
"Those who blew up the Twin Towers were the ones America armed to fight against communism" spreading from the Soviet Union, he said, "and those who are killing Muslims and Yezidi in Iraq are those who received financial support in Syria" to counter the regime there.
"History teaches us this rule: You can build religious groups that (will be) very dangerous, but it will be very difficult to suppress or eliminate them," the Muslim scholar said.
Egypt's grand mufti, Shawqi Ibrahim Abdel-Karim Allam said in his presentation Sept. 8 that "Islam is a religion of dialogue," and that radical extremists are "secular people who proclaim to be religious authorities, even though they are unqualified to interpret religious and moral laws."
These extremists have an "eccentric and rebellious attitude toward religion" that "opens the door to extremist interpretations totally extraneous to Islam," he said.
However, it's not enough to dismiss extremists as having no legitimate religious authority, he said.
"If we do not understand the factors that contribute to the justification of terrorism and extremism, we will never be able to eradicate this epidemic," he said.