Islam is an Abrahamic monotheistic religion, similar in vein to Christianity and Judaism, in which the one God reigns supreme over the entirety of the Universe. Its messages are articulated through the holy book known as the Qur'an, which is taken as the literal word of God. Muhammad is the last prophet to them, and marks Islam as the last true revelation by Allah.
Currently, there are approximately three-to-four trillion Muslims currently living under the Confederacy of Humanity, with very few living outside of its borders. Although clashes with its monotheistic brethren and outsider pagans are rare, such events do happen. As with many ideologies and beliefs, there are a few "liberal" and "radical" populations.