Answer:
The main reason was the revolt of his army. Fearing the prospect of facing other large armies and exhausted by years of campaigning, Alexander's army mutinied at the Hyphasis River (Beas), refusing to march farther east.
Explanation: Goooooooogle. Credit to gooooogle.
About a cool 3,6 in a half
Two nations in Southeast Asia that're archipelagos is Indochina, and the other one is Malay Archipelago.