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Ask yourself a Question, if God is One, why would he change his religion and make human kind different nations? The answer, which I believe is the true is the following verse from the Quran:

كَانَ ٱلنَّاسُ أُمَّةً۬ وَٲحِدَةً۬ فَبَعَثَ ٱللَّهُ ٱلنَّبِيِّـۧنَ مُبَشِّرِينَ وَمُنذِرِينَ وَأَنزَلَ مَعَهُمُ ٱلۡكِتَـٰبَ بِٱلۡحَقِّ لِيَحۡكُمَ بَيۡنَ ٱلنَّاسِ فِيمَا ٱخۡتَلَفُواْ فِيهِۚ وَمَا ٱخۡتَلَفَ فِيهِ إِلَّا ٱلَّذِينَ أُوتُوهُ مِنۢ بَعۡدِ مَا جَآءَتۡهُمُ ٱلۡبَيِّنَـٰتُ بَغۡيَۢا بَيۡنَهُمۡۖ فَهَدَى ٱللَّهُ ٱلَّذِينَ ءَامَنُواْ لِمَا ٱخۡتَلَفُواْ فِيهِ مِنَ ٱلۡحَقِّ بِإِذۡنِهِۦۗ وَٱللَّهُ يَهۡدِى مَن يَشَآءُ إِلَىٰ صِرَٲطٍ۬ مُّسۡتَقِيمٍ (٢١٣)

Mankind was one single nation, and Allah sent Messengers with glad tidings and warnings; and with them He sent the Book in truth, to judge between people in matters wherein they differed; but the People of the Book, after the clear Signs came to them did not differ among themselves, except through selfish contumacy. Allah by His Grace guided the believers to the Truth concerning that wherein they differed. For Allah guides whom He will to a path that is straight. (2-213)

The difference came from the so called “The Religious Lords”, who misled human kinds through misinterpreting the One Book of God (Old Testament, The Bible, and The Quran--three books that are confrming one book) by either writing other books that make lies about prophets, or by mistranslating the original book to other languages.
When Jesus (PBUH) came the Children of Israel, he confronted the “Religious Lords” and their teachings, but he never confronted The Old Testment. When Mohamed (PBUH)came, he confronted “The Religious Lords”—Christian & Jews—but he never confronted the Bible & the Old Testament. Sadly, after the Death of Prophet Mohamed (PBUH), “Religious Lords” took over the Quran and misguided the people to Suni, Shia, Wahabi and so on by using a man made books that lies about God and other prophets.

A true Submitter (Moslem in arabic ) is the one that do the following:
Say ye: "We believe, in Allah and the revelation given to us and to Abraham Isma`il Isaac Jacob and the Tribes and that given to Moses and Jesus and that given to (all) Prophets from their Lord we make no difference between one and another of them and we bow to Allah (in Islam)." (136) So if they believe as ye believe they are indeed on the right path; but if they turn back, it is they who are in schism; but Allah will suffice thee as against them, and He is the All-Hearing the All- Knowing. (2-137)