Caliphates are especially alluring to extremists today, because they're associated with great Muslim empires which previous stretched across the world to the gates of Europe. They are the core of Sunni Islam.
But the caliphates of old which featured in The 1001 Arabian Nights celebrated wine, women and song and they are therefore very different to the caliphate Islamic State wants to establish with its emphasis on the strict application of Sharia law especially on social issues and crime.
We know Islamic State's jihadists are extremely committed, well armed and are attracting thousands of new followers every day. They are also media savvy. So is the announcement of a caliphate sheer chutzpah and hype?
Well, Iraqi security forces have yet to launch a successful major assault to recapture swathes of lost territory including Iraq's second city like Mosul and arguably the jihadists are justified in their claim that the world's newest "nation" has de facto status.
John Cookson has been reporting from Iraq for 25 years for international news channels including Al Jazeera English and Sky News. Twitter: @Newsman1000