The 70th anniversary of the US atomic strikes on Japan has prompted reflection, commemoration, and debate about the ethics of war and the world's nuclear arsenal.

"There's no winning in nuclear war," Maryann Cusimano Love, an international relations professor at the Catholic University of America, told CNA. Hiroshima and Nagasaki teach "how horrific nuclear war is."

"Many folks are not aware of how many nuclear weapons remain with us today and how dangerous these arsenals are," she continued. "That is why the Catholic Church has continued to argue that we have to get rid of nuclear weapons, that the presence of these weapons is very dangerous for human life and very destabilizing."

Seventy years ago, the only wartime use of nuclear weapons took place in the Aug. 6 attack on Hiroshima and the Aug. 9 attack on Nagasaki by the United States.

The Hiroshima attack killed around 80,000 people instantly and may have caused about 130,000 deaths, mostly civilians. The attack on the port city of Nagasaki killed about 40,000 instantly and destroyed a third of the city, the BBC reports.

The attacks took a heavy toll on all of Japan's population, but Nagasaki was a historic center of Catholicism since European missionaries such as St. Francis Xavier arrived in the 16th century. After Japan's rulers closed the country, in part due to fears of foreign domination, Japanese Catholics survived centuries of persecution before their freedom of religion was secured again in the 19th century.

"Catholics were actually worshipping in Nagasaki, in the cathedral, at the time the atomic weapon was dropped. All of the people in the cathedral were instantly killed," Love said.

The England-born Father Peter Milward, S.J., an emeritus professor of English literature at Sophia University in Tokyo, told CNA the atomic bomb strike on Nagasaki meant that "some 10 percent of Japan's Catholics were suddenly wiped out."

Many Americans credit the atomic strikes with ending the Second World War that began for the United States with Japan's 1941 attack on Pearl Harbor. But Love said this interpretation is something that Americans should question.

Analysis of historical documents shows that Japanese leaders made no specific response to the atomic strikes, which were not much worse than the "horrific" firebombings that other cities such as Tokyo had endured. Many U.S. military and political leaders after the war also said the atomic strikes did not hasten the end of the war, Love said.

The entry of the Soviet Union into the war against Japan on Aug. 9 was what prompted Japan's surrender, she said. This fact faded from view during the Cold War, when U.S.-Soviet relations grew tense.

Love said that the atomic weapons' use drew condemnation from the bishops of the time.

In August 1945 the Vatican's newspaper, L'Osservatore Romano, called the Hiroshima attack "a catastrophic conclusion … to the war's apocalyptic surprises." The discovery of the weapon cast "a sinister shadow" on the future of humanity.

"The Catholic Church was one of the very few voices at the time that criticized the atomic bombings," Love continued. The Pope and the Vatican rejected the bombing, as did the bishops of the United States.

"They had the insight from the get-go that these weapons and their destructive power were a violation of our Church teaching and heritage."

This teaching continues today in Pope Francis, whose words against nuclear weapons include a Dec. 7, 2014 message to an international gathering on the weapons.

"Nuclear deterrence and the threat of mutually assured destruction," he said, "cannot be the basis for an ethics of fraternity and peaceful coexistence among peoples and states."

Love said the use of nuclear weapons violates just war ethics.

The just war tradition, which is rooted in Catholic thought and has become largely enshrined in most international law, only recognizes the morality of a defensive war. It also governs strategy and tactics in war, barring violence against civilians and non-combatants, she explained.

"You have to always protect the most vulnerable members of society," she continued. While soldiers are trained for war and have the tools and backup to protect them, this is not true of civilians.

Just war ethics require "discrimination and proportion in use of force." This includes a ban on weapons "that do not discriminate between combatants and civilians."

"There are some types of weapons that can never meet just war criteria. That's why we call them weapons of mass destruction," Love said.

These include atomic weapons, as well chemical and biological weapons. These ethics also apply to conventional weaponry deployed en masse, such as other bombing attacks in the Second World War.

Love said nuclear arsenals still pose "tremendous risks," and not only in a nuclear war. Many people have been harmed in the manufacture of nuclear weapons and by atomic tests. There is a risk of accidental detonation or theft by terrorists, with 100 thefts of nuclear materials every year.

On Thursday, the anniversary of the first atomic strike, the city of Hiroshima held a large memorial service with representatives from 100 countries, including the U.S.

Father Milward reflected that he saw a difference in the "contrasting memory" between Hiroshima and Nagasaki.

"The bombing of Hiroshima was a deliberate target of the American bomb, and the people there are less willing to 'forget and forgive'," he said. Nagasaki was an "almost accidental" secondary target chosen due to weather conditions.  

"Perhaps it is for this reason that the people of Nagasaki, under the influence of Catholicism, are more ready to forgive, if not to forget, than the people of Hiroshima," said Father Milward, 89, who has been in Japan since 1954.

He said the effects of the atomic strikes continue in the Japanese constitution, which severely limits its military.

"I admire the Japanese for their love of peace, in contrast to their former bellicosity which led up to their participation in World War II, and I hope they maintain that ideal in spite of the increasing threats from China and North Korea. But I also hope that they maintain their gratitude to the United States for providing them with the necessary armed umbrella to enable them to uphold their ideal."

Love said the Church in Japan, because of its experience, has become "a real moral witness for why this must never be forgotten, and how the world needs to move towards deeper levels of nuclear disarmament."

She recounted the story of Father Kaemon Noguchi, a Trappist monk who returned home to Nagasaki after the bombing. He visited the rubble of the cathedral and prayed to the Virgin Mary for a sign to help Catholics who might lose their faith in the wake of the attack.

In response, he felt called to go to a particular part of the rubble and dig down. There, he discovered the damaged head of a tall statue of the Virgin Mary-the statue before which he had prayed for discernment in his vocation. Its face was intact.

"It's a very haunting image of both the destruction of this cathedral of Nagasaki but it's also kind of a symbol of how God endures and how faith endures through the intervention of the Virgin Mary, even in time of great suffering."