There is a very big error in that article.

"Yet the west should be able to see the similarities between Islamism (or Islamic revivalism) and 19th-century nationalism in Europe. Both started as a sort of forced march into the future and then they detoured in sinister and destructive ways: fascism then and the jihadi cult of death now."

It really goes from here, 19th century nationalism was a throwback on the tie that binds, the shared past with which people could legitimize a nation, it was inward in nature, nobody wanted the return of Rome or the Holy Roman Empire of Charlemagne. For islamism that shared past would be the caliphate; outward.