It is a total misunderstanding of the teachings of that group’s religious book.
The Crusades was caused by the few that perverted the teachings of the Bible which resulted in the invasion into the Holy Lands.
Now today we have the Qur’an’s teaching being perverted by a few and spreading their lies to those that have not fully and completely read this holy book. As a result we have today’s Jihad which is nothing more than a modern version of the Christian Crusades.
What is required is for those with the true knowledge of the Qur’an to become more vocal and to stop this Jihad. Will they do this? They have not yet, so I seriously doubt it