Is religion the primary motivation and recruitment behind ISIS?

ISIS fighters are motivated by wider political battles between Saudi Arabia and the West

Question: Is religion the primary motivation and recruitment behind ISIS?
Position‹2 of 2: No, politics, not religion, is the primary factor.
Argument1 of 2›: ISIS fighters are motivated by wider political battles between Saudi Arabia and the West

The reasons people join are typified by the ongoing political battles between Saudi Arabia and the West.

The argument

The Islamic State's drive primarily based on its opposition to Western involvement in Saudi Arabia and the greater Middle East. With its large oil reserves, Saudi Arabia has kept a close relationship with the West. The political nature of ISIS is also based on the effects of the United States March 2003 invasion of Iraq. The US occupational authority dissolved the Sunni majority Iraqi military by decree in May, leaving thousands of Sunni officers unemployed, alienated, and enraged. The Islamic State's political nature is also reflected in their goal of generating hostility between Muslim populations across the world and the broader communities they live in. This strategy is what some analysts have compared to Maoist revolutionary insurgency doctrine, forcing Islamic communities across the globe to pick a side and become more inclined to join the struggle.

Premises

[P1]ISIS arose largely from political grievances against Western involvement in Saudi Arabia and the consequences of the 2003 US invasion of Iraq, which alienated thousands of Sunni officers. [P2] ISIS's strategy of polarizing Muslim communities against the societies they live in reflects a political, insurgency-style doctrine rather than a primarily religious aim. [C] Therefore, ISIS's motivation and recruitment are driven primarily by political factors, not religion.

Counter-arguments

ISIS believes that Saudi Arabia's relationship with the West has tainted and theologically warped the wider Salafi/Wahhab movement, something that must restored at all costs.

Rejecting the premises

[Rejecting P1] The political grievances are real and account for the conditions rather than the ideology. Disbanding the Iraqi army supplied recruits, military expertise and resentment; it does not explain why the resulting movement organised itself around a caliphate, apocalyptic prophecy and a particular reading of Islamic law. [Rejecting P2] The polarisation strategy is documented, and being strategically effective does not make it non-religious. The group's own material frames that polarisation in explicitly theological terms — as forcing a choice between belief and unbelief — so tactics and doctrine are not separable here. [Rejecting C] The dichotomy is the argument's central weakness. Political conditions and religious ideology are not competing explanations of one fact: grievance explains why the ground was fertile, doctrine explains the particular form the movement took and its appeal to recruits with no connection to Iraqi politics at all.