Unlike Christianity, which preached a peace that it never achieved, Islam unashamedly came with a sword.

In the course of his long life he would master an astonishing number of languages so that for example when writing about the Middle East he relied not only on accounts in Latin and Greek and the Western vernaculars but consulted Arabic Turkish Persian Hebrew Syriac Armenian and Georgian sources as well. "Balkan Cities--Yesterday and Today. 4 (1977): 1-12.

His best known work is his three volume A History of the Crusades (1951-54).