The question that I have is why do they have such massive support, their ranks are swelling from all over the world.
Maybe this is a blessing in disguise (all militants flocking to one geographical location).... something to ponder
It appears to be mix of reasons.
Undoing the thoughtless western worlds post WW1 middle east divisions from political to religious.
The old Ottoman Empire was partitioned with absolutley no regard for Religious or Ethnic divisions.
Therefore repartitioning along religious lines makes sense to many.
A caliphate based on religious lines, governed and ruled by faith is the dream of many Muslims, free from western idea's, free from what is deemed as Western "oppression" of their faith.
Oppression is regarded as many forms, adhering to the laws in many western countries, re: dress code, womens rights etc etc, and the many inumerable small nuances of western culture are often viewed as forms of "oppression" of the faith.
In all religions there are also tales of prophecy of the end of times, or the arrival of some or other prophet or event.
The establishment of a caliphate goes towards fulfilling a prophecy of the coming of the "Mahdi" after the fall of violent leaders (despots and dictators).
Foretelling of battles in Syria for the soul of the faithfull, Muslim against Christian. Yadda , yadda etc etc
The common calling card driving the growth of their support.
The violence portrayed is a powerful message, "see what happens to those who do not believe and follow".
Its psychological warfare performed for those areas under attack, and it is guaranteed to instill fear in those who think of opposing them.
It is also powerful propoganda , as it got attention from western countries, and has garnered a response in the form of military action.
Military action that can be seen once again as oppression of the faithfull, oppression of the caliphate, and it all falls neatly into the foretelling of the prophecies.
Prophecy and faith, intermingled and inseperable, a powerful motivator, a dangerous mix, something the west fails at times to understand.