With the death of Saturninus and self exile by Marius in 99 BC, a period of relative calm slipped into Roman politics. The calm wouldn't last long, however, and a new Tribune in a mold similar to the Gracchi brothers, came to the forefront. Marcus Livius Drusus was actually the son of a political opponent of the Gracchi, but he took up the cause of the Italian people with a new zeal. Drusus, among several reforms, attempted to distribute land and citizenship for the Latin rights Italian allies.
His objective was actually the preservation and strengthening of the Senate, but in practice it didn't appear as intended. He hoped that by including the Italian allies as voting citizens, he would bring in a new voting force loyal to the traditional Senatorial authority and not to the demagogue tribunes who used popular ideas to incite the Roman mobs. Unfortunately for him, and as a result of their own short sightedness the Senate saw things in a completely different light.
As Tribune in 91 BC, Drusus reformed the corrupt court system by promoting 300 of the top Equites into the roles of the Senate, thereby doubling the number of Senators. This altered the financial stake of potential jury members and helped to balance the system. New land and grain laws were introduced to win over the rural and urban plebes respectively. And finally, he introduced the citizenship law that would end in his demise, and open revolt.
After much political wrangling, as was common in the late Republic, Drusus' laws were eventually dismissed, but he persisted in trying to push them through. His actions and proposals, which were holding the angry Italian allies in check as they hoped for a political resolution to their complaints, led directly to his murder late in his term. Stabbed in the thigh by an unknown assailant, and certainly an affiliation of the elite, the death of Drusus fueled the flames of revolt.
Led chiefly by the Marsi and the Samnites, several Italian tribes, who for 2 decades had been trying to gain citizenship through the political system, decided enough was enough. A new state, in the image of Rome, was set up with its capital in Corfinium. A Senate complete with Consuls and Praetors was organized mimicking Rome, only without Rome as a part. Back in Rome itself, armies were organized to oppose this new breakaway Republic and by 90 BC, the war was on.
Things went badly for the Romans initially. In the north, Marius had returned to help his Consular relative, P. Rutilius Lupus, whom held the overall command. One mistake after another led to defeat in several battles until Lupus was finally killed in action. Never one to miss an opportunity, Marius took full command of the northern campaign and the impact was immediate. Within a few short months, the northern Italians were on the defensive and the focus of the war shifted to the south. The southern Italians captured and sacked several towns before the Romans could intervene. First led by Lucius Julius Caesar, several defeats eventually gave way to a victory that saw Caesar hailed as an imperator in the field. But the situation was far from over, and things were still in doubt when Lucius returned to Rome for the elections of 89 BC.
In order to bring the revolt to a close, Caesar instituted the Lex Julia. It was a law that granted full citizenship to any Italian ally who did not revolt, and to any Italians that were currently in a state of revolt who would immediately lay down their arms. Its passage essentially granted the Italians the victory they initially set out to get, but many refused to lie down their arms. The following year resulted in more political wrangling than anything, but nevertheless, the war continued. By this time, Sulla had returned from a praetorship in Cilicia and was granted command in the south. As a slight against Marius another political opponent, Caepio, was placed in command of the north, but he was soon killed in battle; leaving Marius with another opportunity for prominence.
Gnaeus Pompeius (father of Pompey the Great) took over command of the north and laid a punishing siege on the Italians at Asculum. After a protracted hold out, Pompeius captured the town and the defenders were brutally dispatched. Sulla meanwhile methodically defeated the opposition in the south and he returned, at the end of the year, to stand for the Consulship. Sulla would win the office for 88 BC and Gaius Marius, aged and perhaps in the early stages of mental illness, reacted horribly.
The Social War came to an end with the Italians essentially gaining everything they wanted, even though they had been defeated in the field. Various mopping up activities would take place, but new developments in the east would create an entirely new scenario. Mithridates of Pontus saw the Roman internal struggle as an opportunity for his own expansion and he began to press against Roman territory. The conflict over who should command would send the rivalry between Marius and Sulla to new heights, which would eventually result in bloody proscriptions and violence against both sides.