It could be argued that Islamic political unity represents the essence of the battle. Consequently, the idea is besieged by all parties who are hostile to the Islamic project, or against it, in order to diminish the status of political unity of the Ummah in the Islamic discourse and remove it as an essential maxim of the Islamic Movement.

The maxim of an Islamic Caliphate and a United Islamic State represents the dream of millions of Muslims; it is the banner that brings together all Arab and Muslim countries, and the most prominent title of the rising history of the Islamic Ummah. This maxim is strong enough to gather the Ummah, unite its orientation, and motivate it to realize its own unity. Therefore, this maxim has been besieged and the Islamic Movement has been put under pressure to express this maxim only implicitly in its discourse. Moreover, the maxim itself is considered to be hostile to the existing territorial nation-state.

http://www.onislam.net/english/shariah/contemporary-issues/critiques-and-thought/431940-new-islam-a-project-without-a-caliphate.html