Dr Houlihan is a historian interested in the study of religion and violence. His publications include a book entitled Catholicism and the Great War: Religion and Everyday Life in Germany and Austria-Hungary, 1914-1922 (Cambridge University Press). He is currently working on a new book, looking at the global history of the Catholic Church during the First World War.
- European and global history since 1789
- Christianity, especially Catholicism
- First World War
- Second World War, including Nazi Germany and the Holocaust
- Religious violence and peace-making
- Peace and humanitarianism
Dr Houlihan has given public lectures around the world.