A major religious group, one of the three Semitic religions. Believes in complete subjugation to god, and that the Koran is the immutable revealed truth which shall be for all time to come.
Unfortunately, a large section of muslims take this to mean that the Koran, being of god, shall prevail over all laws of man. For example, they believe that democracy is the law of people, not god, and so it is not for the devout muslim. Further, the contents of the Koran (evolved several hundred years back in a nomadic, warlike, women-suppressing community) are believed to be equally valid now.
Thus, it is extremely hard to find a truly democratic Muslim-majority country (perhaps Turkey is an exception). In consequence, most islamic countries are dogged by theocracy, civil war, decimation of minorities (look at the plight of hindus in Pakistan and Bangladesh) or more recently, the killing of most pigs in Egypt, ostensibly in the name of H1N1, but really because the pig-growers were all coptic christians.
In countries where islam is dominant, there is war between factions or between secularists and islamists. In the countries where they are minorities, they have problems with the majority community (no matter which community this is--look at Mindanao, where one of the most pacific people, the Philippinos, are finding it difficult to coexist because of the Abu Salem group).