I think a series of crippling natural disasters is the answer.
Southeast Asia commanded the sea Lanes between India and Asia
Answer:
OCTAVIAN GETS TO THE POWER After the death of Caesar, the three Socialists fell into the hands of a politician-general belonging to Caesar's circle. One of Antonius Caesar's commanders, Lepldus, was the leader of the cavalry, and the young but more purposeful Octavian was Caesar's nephew, the dictator's official heir, whose uncle took control of the events. Winning the shackles of power, he was among the contenders for power. They conspired to seize power: this was the second triumvirate (43 BC). The following year they defeated the (Philippi, 42 BC) and then divided among themselves the power over the empire: Octavian to the West, Antonius to the East, and Africa to the Republicans. Lepidus soon faded into the background, and then Octavian and Antonius continued to fight each other for monopoly. Another civil war became inevitable. Antonius relied on Hellenistic Egypt. To the last Egyptian queen, VII. Because of his love affair with Cleopatra, many feared that Antonius E would not appreciate Roman tradition and that the center of gravity of the empire would be to the east. For this reason, the majority of the Romans supported Octavian. The decisive clash took place at Actium (31 BC), and Octavian won the naval battle. He became the power.
