Final answer:
Alexander the Great turned back due to his troops' exhaustion, a near mutiny, and the daunting prospect of further conquests with diminishing returns. The arduous journey back and his untimely death from poor health ensued.
Step-by-step explanation:
After eight years on the march, several significant factors contributed to Alexander the Great's decision to turn back. His troops were exhausted and had grown weary of the continuous campaign. They reached a point where they refused to push further into India, as venturing towards the Ganges River Valley seemed an insurmountable challenge and offered no clear benefit.
Additionally, after consulting an oracle and facing a near mutiny of his forces, Alexander decided to lead his army back to the heartland of Persia. The return journey proved arduous, culminating in a deadly traversal of the Makran desert, which claimed more lives than the entire Indian campaign. Upon finally reaching Babylon, Alexander's health declined rapidly due to a combination of injuries, alcohol, and exhaustion, leading to his premature death.