Muslims had confronted many religions and ethnic cultures, mainly Christianity, Judaism and Zoroastrianism, when they controlled 3the regions of Iraq and Sham. They entered in cultural interaction by founding new cities such as Basrah and Kufa in this region and by moving to the settled life. The fact that they felt the need to define their beliefs led them to look for various theological discourses. In this search, the followers of Islamic theological school of Mu’tazilah succeded under the leadership of Wasil b. ‘Ata and ‘Amr b. ‘Ubaid who were the pupils of Hasan al-Basri. The Mihna events made a negative impact on the Mu’tazilah which emerged through scholars such as Abu’l-Hudayl al-Allaf, Bishr b. Mu’tamir and an-Nazzam. This resulted with a period of weakenning. Even the efforts of Abu Ali al-Djubbai, his son Abu Hashim and Abu’l-Qasım al-Ka’bi could not stop this `falling down`. The state of Khwarazmshahs became the last castle of Mu’tazilah, and afterwards `pure` Mu’tazilah school disappeared with the last blow of Mughal invansion.