As the legal arrangement for the triumvirate between Octavian, Antony and Lepidus (even though he was no longer an official part of the arrangement) expired at the end of 33 BC, 32 BC turned into a year of political posturing and strained anticipation. Without legal triumvir powers, Octavian technically reverted to no more than a leading member of the Senate, and the Consuls for 32 BC, Cn. Domitius Ahenobarbus and C. Sosius both Antony supporters, sought to bring Octavian down.
While Octavian was outside of Rome, Sosius launched an attack on Octavian's legal position to the convened Senate. Though the precise nature of the attack is unknown, it's safe to assume that the Antony supporters definitely wished to limit Octavian's power and position. What they surprisingly failed to count on was Octavian's support among the army and his boldness in using it. When he returned to Rome he called the Senate to meet, backed by an armed escort, and proceeded to turn the tables on the sitting consuls. Launching his own attack on Antony, it was clear that the Roman world was once again heading towards civil war. In Rome, despite Octavian's lack of legal right to rule, it was also quite clear that he was in fact, the unchallenged leader of the west. Not even Antony's supporters attempted to dispute him, and many Senators (up to 300) fled to Antony, rather than attempt to put up a false front that all was well.
News soon returned to Rome that Antony intended to set up a separate eastern Senate in Alexandria to govern the eastern part of the empire. He also officially divorced Octavian, denouncing her in favor of the foreign Queen, Cleopatra. Octavian knew that war was coming, but now needed to rally support among the masses. By fortunate circumstances, two important supporters of Antony had defected to Octavian's cause and returned to Rome about this time. L. Munatius Plancus and M. Titius brought word to Octavian that Antony's will, now deposited with the Vestal Virgins, contained incriminating evidence of Antony's anti-Roman, and pro-Cleopatra stand. Both men, it seemed, had been witnesses to the document, and Octavian illegally seized the will from the Vestals. In it, Antony recognized Cleopatra's son Caesarion as Caesar's legal heir, propped up his own eastern appointments by leaving large inheritances to his children by Cleopatra, and finally indicated his desire to be buried with Cleopatra in Alexandra. Though the first two matters wouldn't be considered all that unusual, it was the third that set off a firestorm of anti-Antonian sentiment. Already suspecting him of abandoning Rome for Cleopatra, the people clearly saw his rebuttal of Roman cremation tradition and the favoring of eternal burial with Cleopatra as proof of him falling under the Queen's sway.
Octavian seized the opportunity to gain from the people's sentiment, and encourage the rumors that followed. If the people believed that Antony had every intention of making Cleopatra the Queen of Rome, and by virtue of his new eastern Senate would move the capital to Alexandria, it could do nothing but favor Octavian. He was reserved in his intentions, however, and knew that Antony still had some supporters. Civil War too, simply for the benefit of Octavian would never be popular. He also wished to make it easy for Antony supporters to willingly switch sides without seemingly being disloyal. Rather than announce war with his rival Antony, Octavian declared war on the hated Queen Cleopatra, the perceived cause of all the trouble. As both sides geared up for the conflict that would seem to be the largest and costliest ever for the Roman state, a remarkable show of public support took place. The people of Italy and the western provinces swore on oath of loyalty directly to Octavian, rather than the Roman state. Though this was likely a greatly orchestrated political maneuver by Octavian, a now brilliant politician, it had the desired effect of at least giving him the public support he needed to take the nation to war. While by no means presenting Octavian with any sort of legal power over the Roman world, it did help to clarify for everyone that not only did Octavian maintain power through the legions, but also through the good will of the Roman people.