Hostilities broke out after Octavius opposed Cinna's attempts to distribute the Italian citizens enfranchised after the Social War into all voting tribes and to recall the outlawed Gaius Marius from exile.
He began touring Italy to recruit men, while the Senate in Rome replaced him with Lucius Cornelius Merula, a priest of Jupiter, in the consulship.
Octavius won the support of the two other Roman generals in the field in Italy, Metellus Pius and Pompeius Strabo; the Samnites, who were formally at war with Rome, joined Cinna.
More concretely, Sulpicius passed legislation depriving Sulla of his command against Mithridates and illegally assigned it to his old rival, Gaius Marius, who was at the time a private citizen.
[2] In response, Sulla induced his troops at Nola to restore order in the city, arguing that Sulpicius' bill was an assault on the consuls' authority and that of the people who had elected them.
[9] Sulpicus' laws were invalidated on the basis that they were passed by force, restoring Sulla to the command against Mithridates and annulling the distribution of new citizens among the thirty-five existing tribes.
His broad unpopularity,[10] however, was keenly felt when his candidates were all rejected at those elections, which chose Gnaeus Octavius and Lucius Cornelius Cinna as consuls-designate.
This failed as Sulla ignored the tribune's demands that he return to Rome and was regardless immune from prosecution due to his proconsular imperium;[13] he departed rapidly for the war on Mithridates.
[19] Because the restrictive religious obligations of the priesthood, Merula was largely unable to execute his consulship, leaving Octavius as de facto sole consul.
[20] Calling on them as citizens to vindicate his election and arguing that not to do so would create a tyrannical senatorial oligarchy who would be able to rule without reference to the people, the soldiers lifted Cinna back to his curule seat and restored his symbols of consular office.
Pompey Strabo, who had been called by Octavius and the Senate to defend the city, encamped near Rome at the Colline Gate but remained aloof to play both sides.
[23] Pompey Strabo, unable to reach an agreement with Cinna and Marius, fought Sertorius near the Janiculum, while the Senate sought to raise more men by offering citizenship for all Italians who had surrendered.
The Senate then instructed the proconsul Quintus Caecilius Metellus Pius (previously praetor in 90 BC)[24] to make peace with the Samnites he was fighting if possible with honour and relieve the city.
The Samnites pushed for extremely generous terms which Metellus rejected; Cinna, in separate negotiations, instead gave in to all their demands, securing their support.
Octavius, refusing to flee the city, was then killed on his curule chair set up in the Janiculum; his head was then cut off and displayed on the forum.
Cicero, more contemporaneous and speaking to men who lived during the Cinnan regime, indicates that Cinna and Marius targeted only political enemies and did not threaten all of Rome's inhabitants or otherwise sack the city.
[38] At the end of the year, Cinna and Marius presented themselves before the comitia centuriata as the only candidates for the consulship and were duly returned in irregular elections.
For all his rhetoric at the start of the year 87 BC, Cinna and his allies seemed very willing to continue the existing state of affairs and made no efforts to complete a full registration.
[42] The threat of Sulla in the east remained when the Roman army sent to replace him in command fell into disarray after its general, Lucius Valerius Flaccus, was assassinated by his quaestor.