Why did Octavian declare war on Cleopatra VII rather than directly on Mark Antony?

Octavian declared war on Cleopatra rather than Mark Antony primarily as a strategic political maneuver to avoid the appearance of initiating another Roman civil war.12

By framing the conflict as a war against a foreign queen, Octavian sought to unify the Roman people against an external threat rather than against a fellow Roman leader. This strategy was supported by a campaign of propaganda that depicted Antony as being under the dangerous influence of Cleopatra. Octavian fueled public outrage by claiming that Antony intended to transfer Roman territories to Greek control and by seizing Antony’s will, which allegedly proved his subservience to the Egyptian queen and his desire to be buried in Alexandria.12

By declaring war on Cleopatra, Octavian effectively cast Antony as a traitor who had abandoned his Roman identity for a foreign power, thereby legitimizing his own cause and securing the allegiance of the Roman population.12