This is what I did for the " Islamic " part of my world. There are definitely other gods, and the gods of those pantheons have made the same claims ( They are the true gods and saviors of humanity ) to their chosen peoples. The following is a sample of just three conflicting faiths in a region about the size of the Middle East. Sorry about the length.
Sadian & Yemari Religion
Qadarism
For nearly 1000 years, humanity struggled to survive in a hostile, barbarous world...Until the prophets came. They came to the men of the North, the South, and here in the East. The prophets spoke of the Covenant of the Gods and it's promise to lead humanity to a new golden age. But according to the Sadians and Yemari people these were false prophets...
The true and only prophet wandered out of the sands of Sadia in the year 999, Prophet Mamoudar Al Qadar, delivered to his people the true Covenant from the Enlightened Ones. The Enlightened Ones promise paradise through our prophet...
The Enlightened Ones are the TRUE gods, and Mamoudar Al Qadar is their prophet....
" Now that we are amongst friends, I can tell you that the Pashemites and my people have been at war since the first centuries after the Great War. My people, like the majority of other enlightened people of Sadia, chose to follow the Prophet Mamoudar Al Qadar and his Law of the Covenant between men and the enlightened gods. By following the Law of the Covenant, men would find peace and once again live in paradise. The Pashemites chose to follow the Deceiver Molech, a former student of the prophet, and the prophets brother. Molech allowed his heart to be turned towards evil by the temptress and whore of the gods, Ishat. Together they raised an army to wipe out the Prophet, and have men ruled by Devils, creatures that Molech claims to be the true creators and lords of men. Molech was defeated, and his followers driven to the Isle of Pashem, where they still live today, plotting the destruction of enlightened civilization. "
Qatari Religion
Omadism
In 979 CE sheik Faisal Omad ( A legendary desert warrior from the wastes of Sadia ) led his tribe to the Al Qatar region after receiving visions from agents( commonly called the Nephilem ) of the Enlightened Ones . The sheik was told to record the words of the Covenant, and to teach and prepare the people of present day Al Qatar for the arrival of a prophet from the West. The Prophet did arise from the West 20 years later, and the people of Al Qatar fought under his banner against Molech and Ishat.
After the death of the prophet and his later rise into the heavens, sheik Faisal was also taken by the Enlightened ones.
Qatari believe that sheik Faisal Omad was the first prophet, and hold to his version of the covenant, claiming that it is the original. The Qatari faith is known as Omadism, and is reluctantly tolerated by the rest of the Enlightened peoples. After two centuries of religious conflict ( 1060 to 1260 CE ), it was agreed that both faiths could coexist under the common belief of the Enlightened Ones.
Pashemite Religion
Pashemism
Molech, being tempted by Ishat, chose to follow the lords of evil that dwell in the 9 Hells. Molech's birth name was Sarmal Pashem Al Qadar. He was the youngest brother of the prophet and the first to follow the prophet. It is said that the young Sarmal was jealous of his older brother, and one night was visited by Ishat. She convinced the young Sarmal that the true guardians of humanity resided in the 9 Hells, and that they created men, thus were the true path to paradise.
Young Sarmal's jealously grew into hatred, and with his mistress Ishat at his side, gathered followers and challenged the prophet. With the power of the 9 Hells at his command, Sarmal took the name of Molech Pashem and met the prophet and the armies of the faithful in battle. Molech fought hard and even slew his brother, but the power of the Nephilem that fought with the prophet proved stronger. Molech gathered his remaining followers and retreated to the island now known as Pashem.
Upon Molech's death at 126 years of age, his soul was taken by Ishat to the 9 Hells, where he resides in the court of his patron Ashmodai. Before he left, Molech delivered to his people the Covenant of Ashmodai and fathered 24 children with his mistress Ishat. The 6th born son, Ishamar Pashem became the first " Pashem " of the kingdom, and slew his other brothers to secure his hold on power. His 6 sisters became part of his harem and gave birth to successors. The Pashemite religion recognizes the Lords of the 9 Hells as the Enlightened Ones, with Ashmodai ( Asmodeus in the Promethian tongue ) as the " Lord of Hosts. "
The Enlightened Ones
The Enlightened ones are said to be the true saviors of humanity. They are the culture bearers and the architects of civilization. It is written that the Enlightened Ones guide humanity on a thousand thousand worlds, protecting men from the devils of the 9 Hells and the demons of the Abyss. They promise paradise to all that follow their teachings.
The Enlightened Ones:
Ea ( Patron of humanity, the architect of civilization, Lord of the 1st paradise )
Uzekel ( The messenger, patron of the written word, lord of the 2nd paradise )
Gabrahl ( Gaurdian of the 7 paradises, lord of the 3rd paradise )
Astarte ( Mother of humanity, giver of divine magic, queen of the 4rth paradise )
Malek ( Lord of the Nephilem, lord of the 5th paradise )
Ulsefar ( Patron of music and art, lord of the 6th paradise )
Shemra ( Lady of the shield, guardian of humanity, Queen of fate, Queen of the 7th paradise )