- "There is no god but God. Muhammad is the messenger of God" (as was Adam, Abraham, Moses and Jesus). That quote is called the creed (Shahada) and takes on spiritual meaning as one of the 5 pillars of Islam
- The Five Pillars of Islam, which are obligatory acts of worship (1) the creed (Shahada), (2) daily prayers (Salah), (3) almsgiving (Zakat), (4) fasting during Ramadan (Sawm) and (5) the pilgrimage to Mecca (Hajj) at least once in a lifetime)... and following Islamic law (sharia), which touches on virtually every aspect of life and society, from banking and welfare to women and the environment.
- The religion was created in the 7th century in Mecca, by Mohamed sharing his visions in the form of the Quran, which is the primary scriptures of Islam and the verbatim word of God (but there are many ancillary teachings that impact the belief as well). The cities of Mecca, Medina and Jerusalem are home to the three holiest sites in Islam.
- God is merciful, all-powerful, and has guided humankind through prophets, revealed scriptures and natural signs, as well as intervention in all outcomes. While Islam teaches that the righteous are rewarded with paradise and unrighteous punished in hell, it also believes that God (Allah) guides everything, and thus almost everything around us is the will of Allah, and you're either working towards his will, or away from it. Allah is more involved in the day-to-day than Jehovah or God is to Jews/Christians.
- Islam believes in social justice (as they see it), and a hierarchy where other Muslims are to be treated differently (better) than the other Abrahamic religions, which are much better than pagans or atheists. Islam replaced tribalism with Religionism, and "the Nation" is far less important than in other western cultures: think "God, Family, Country", as "Godliness, Family, Other Muslims, Country, Infidels" -- with infidels not covered by the rules governing how you treat other humans (even to the point of starvation cannibalism isn't a crime). That's not completely how it is practiced by all Muslims, but that is how it is sort of coded in the religion.
- Because Sharia is a legal system, and Allah impacts rules about all aspects of life, including governing interaction with others -- Islam is not only a religious system, but a political and legal belief system as well -- much more than something like the 10 commandments or even Leviticus.
- It is the world's second-largest religion with over 1.8 billion followers known as Muslims. Muslims make up a majority of the population in 50 countries -- and in most of them, there is little or no freedom of Religion. Again, Religion and Politics intertwine and the purpose of government is to further the will of Allah.
- While Islam is big and widespread, and is the fastest-growing major religion in the world, it was once world (region) dominant during the Caliphates (8th - 16th century). They had the most military power, science, knowledge, and were the center of the world trade. But while they are the second most popular religion, they have contributed less (in modern times) and have less political influence, economic and military power than Christians, Communists or Jews, and are one of the least influential based on the influence of the 50 countries that they control. They have the resentful fallen empire chip-on-their-shoulder that goes with that.
Islam has fallen far behind economically, culturally, scientifically, and so on, since the middle ages. Since everything is the will of Allah, this sets up quite a religious conundrum (similar to the Jews questioning why God would allow the Holocaust to happen to his chosen people). If God is good, and demands equality -- then why is there imperialism, inequality, and most importantly, why didn't Islam win?
Many Muslims see it as Allah let it happen not because Muslims followed the rules of Islam (which resist order, authority, and meritocracy), but because they were not pious or dutiful enough to the word. This, economic/cultural disadvantage, western oppression, the conspiratorial nature of the Middle East, all contribute to why it might be easy(er) to radicalize some Muslims than other religions, though radicals come in all flavors.
The truth is their system of beliefs put them in conflicts that thwart their own progress -- and they see progress itself as varying from traditions. The West's capitalism and progress oriented liberalism (progressivism) enabled them to outperform Islam's more socialism-like regressivism. But many in Islam prefer the comforting lie, that it was not enough Islam, to the uncomfortable truth, that it was too much. (This is similar to why Japan could make leaps ahead of the west, before boomeranging back to simpler and more traditional times. Or why China often resisted progress for tradition, for thousands of years).
Almost everything Muslims did to establish authority or bureaucracy created a hierarchy that was seen as thwarting the Social Justice demanded by Mohamed -- and generally the countries that thrived best under their control (like Iran), where the ones that were run by locals, a little less devout and extreme than the purest Islamic Arabs.