Muslims, much like the followers of many cults and man-made religions (such as the Bahai Faith), believe that every culture and people have been given prophets and messengers from God, and, according to Islam, these messengers or prophets practiced Islam, which basically means submission to the one true God, and they preached that there is only one God to their peoples and cultures. (The five pillars of Islam are said to be the marks of submission to God, which is ironic because God only revealed them to Mohammed, not to anyone else before Mohammed, so how someone could submit to God before him I have not a clue).
What else is ironic is that hardly any culture or people other than Christianity and Judaism believed in one God - in fact, this was the big distinguishment between God’s People and the gentiles. The gentiles considered Christians and Jews to be poor people because they only had one god, while they had so many gods and goddesses (ironically, these gods were more creature-like than divine, having human emotions and errors, and it is said that many were actually demons in disguise). This is why Judaism feared assilimiation during the Roman Empire, and that is why so many Jews hated the Empire and were waiting for a Messiah who would quite literally destroy the Romans, and thereby, restore the Kingdom of Israel. But I’m getting off topic.
Some Muslim scholars point to a paraoh in Egypt who believed in one god and say, “See, he believes in God! It is clear proof that there were many messengers sent by God before Mohammed, even though we do not know who they all were.” However, this would be historically false, because the world was steeped in polytheism. Some scholars even point to the rampant polytheism of the ancient world as proof of Islam before Mohammed, however this would be like saying the Catholic Church corrupted the Bible simply because not all the verses are in favor of someone’s own beliefs: it makes no sense, it shows dishonor toward history, and it shows a lack of understanding of culture and religion. Other scholars point to the creator-god of various religions and say this is proof for Islam, however how polytheism can fit into monotheism is quite beyond me.
Again, it was Christianity and Judaism who, from among many religons, believed in only one God. Muslims scholars could point to our prophets and apostles as proof that Islam was practiced and spread before Mohammed, however this would be false given the fact that neither our prophets nor apostles practiced the five pillars of Islam, nor did they acknowledge the God as portrayed by Mohammed and named Allah, nor did they preach only one God, but rather, the prophets preached repentence and a new covenant and the apostles preached Jesus Christ. (There is an instance in Acts where the apostles do preach one God, however, this was to win the gentles over to Christ; they had to start at first pointing out the oneness of God, using the gentles’ philsophy to do so (“I have become a gentle to convert gentiles…”), and then guide the gentiles to His Son, Jesus). I don’t know of any other religions other than Judaism or Christianity that proclaimed one God. Certainly there were branches and sects that came from Judaism and Christianity - like the Christians who turned to gnosticis or the Essence community - that proclaimed one God, but they weren’t gentiles. And I know that many Arabs believed in Allah before Mohammed, but they practiced polytheism, not monotheism.
Ironically, Mohammed coming suddenly on the scene in history and saying Allah was God is almost like the apostles who pointed to an altar to “an unknown god” and preaching that, what the gentles worshipped unknowingly, they had come to preach who He was: the one God, Creator of all things. This is ironic because Mohammed is basically - perhaps even unknowingly - copying Christianity. However, I don’t know if this actually true. Though it’s true he did copy from many religious text, I don’t know if he was sincere or insincere in his preaching. But it’s kind of like Medjugorje: Maybe the seers really did recieve an apparition at first, but than they turned bad and now are faking mysticism; maybe, too, Mohommed really did receive a message from God to convert, and he wanted to share it with others, but than he became corrupted. (Sorry about bringing Medjugorje into this). I really don’t know the man’s heart, though, so I try not to judge. And I think I went off-topic again. Sorry.