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The Islamic concept of sovereignty differs from the western principles of international custom and law established by the Treaty of Westphalia. An important element of this is the Ummah — the community of Muslims as a whole. Devout Muslims consider that there is no division between religion and politics and so government should be based upon the Qur'an, following the word of God in a unified way, as in the first Caliphate.
References
Amin Saikal (2008), "Westphalian and Islamic Concepts of Sovereignty in the Middle East", Re-envisioning sovereignty, Ashgate, ISBN978-0-7546-7260-9