The author is absolutely correct in his view that WWI set off great and far-reaching changes in society, Christianity and Islam.
I don’t know if leaders of the day saw it as a “crusade” though. The propaganda of the time certainly used religious imagery, but my favorite books on the subject by Tuchman, Max Hastings (and others) all point to the balance of power questions, alliances, naval power in the quest for colonial dominance, and military planning - as the motivations and direct causes of the war.
The “Cousins War”, that wrecked the civilization of Europe. Gave rise to Bolshevik Russia and eventually Nazi Germany.
Barbara Tuchman’s ‘The Guns of August’ is a great book on WWI. I read Keegan’s ‘The First World War’ as well.
One theme you often see is the difficulty of figuring out why Germany and Austria decided to go to war over the assassination.
I guess a land grab for the disintegrating Ottoman Empire makes as much sense as anything else.