He was Distinguished Professor of Ethics and Human Development at the Georgetown University Walsh School of Foreign Service, a senior fellow at the Berkley Center for Religion, Peace, and World Affairs, and the former editor-in-chief of the Jesuit magazine America.
[1] His areas of research included nuclear disarmament, nonviolence and just peacemaking, Catholic social teaching, and ecumenical public advocacy.
An active outdoorsman from his youth to middle age, he loved camping, hiking, and spending as much time as possible in the natural world.
[6] After Pope Francis, under the direction of Cardinal Peter Turkson, hosted a conference—Prospects for a World Free from Nuclear Weapons and for Integral Disarmament—at the Vatican in November 2017.
[12] In broader ecumenical efforts, Christiansen served as a consultant to the Pontifical Council for Promoting Christian Unity for the Mennonite-Catholic Dialogue, honoring Mennonites as members of the historic Peace Churches.
During his tenure as editor-in-chief, he exhorted James J. Martin SJ to travel to the Holy Land for a planned book, Jesus: A Pilgrimage.
[18][19] In 2013, Christiansen returned to Georgetown University in a full-time role as a senior fellow at the Berkley Center for Religion, Peace, and World Affairs and Distinguished Professor of Ethics and Human Development in the School of Foreign Service, posts he held until his death.
Christiansen had a deep personal interest in the pastoral needs of people in residential nursing facilities or aging in place at home, and he visited those in long-term care when he was able, hearing confessions and celebrating the Eucharist.
His 1982 doctoral dissertation at Yale was titled "Autonomy and Dependence in Old Age: An Ethical Analysis" under the direction of Sister Margaret Farley R.S.M., and he retained a lifelong attentiveness to people experiencing issues attendant with such care.
His death followed a long period of physical challenges over several years, during which time he had kept up an ambitious schedule, because he thrived on writing, editing, prayer, Mass, visiting the sick and older people, teaching, lecturing, reading, and enjoying lively interaction with colleagues, students, and the printed page.
Other articles appeared in Popoli (Italy), Projet and Christus (France), Razon y Fe (Spain), Mensaje (Chile), Faith in International Affairs, Ecumenical Trends, and Seminary Journal (USA).