Robert Spencer expertly explains. He concludes his article with these words:
The desire to restore the caliphate ultimately highlights the expansionist, imperialist, totalitarian, globalist aims of the jihad movement, even as today it presents itself as a defensive action against Western evils. This is, I believe, a crucial point for our understanding the enemy properly, so that we can formulate the proper defensive responses. If we don’t understand what we’re up against correctly, we will not defend ourselves properly against it. And that is, unfortunately, in many ways the fix we’re in today.