The author makes an interesting point about the relevance of the Crusades to today’s problems with jihadis: up until the 19th century not 1 in a million Muslims would speak of The Crusades. That began to change when the Dar al-Islam fell behind the Dar al-Harb and needed an explanation. The answer: blame The Crusades. The issue metastasized upon the creation of Israel, when Dar al-Islam lost territory – making their relative impotence too painful to bear and too difficult to explain. The addendum to the answer: also blame “the Jews”.
It’s not unlike the Brezhnev Doctrine – once conquered, no territory shall ever be lost to the enemy.