Sentence:  <WSD>Christianism</WSD> is an ideology, politics, an ism. The distinction between Christian and Christianist echoes the distinction we make between Muslim and Islamist. Muslims are those who follow Islam. Islamists are those who want to wield Islam as a political force and conflate state and mosque. 
Meaning of the word marked with <WSD> tags:  Christian fundamentalism. (from 21st c.)