While Marius was away in the east and after he returned, Rome had several years of relative peace.
But in 95 BC, Rome passed a decree, the Lex Licinia Mucia, expelling from the city all residents who were not Roman citizens.
In 91 BC, Marcus Livius Drusus was elected tribune and proposed a greater division of state lands, the enlargement of the Senate, and a conferral of Roman citizenship upon all freemen of Italy.
But after Drusus was assassinated, many of the Italian states then revolted against Rome in the Social War of 91–88 BC, named after the Latin word for ally, socii.

Marius, rather humiliatingly, had to serve as a legate with his nephew, the consul Publius Rutilius Lupus.
Lupus died in a Marsic ambush on the River Tolenus.
Marius, who was leading another column of men, crossed the river at a different location and captured the Marsic camp.
He then marched on the Marsi while they were busy stripping the corpses and dealt with them accordingly.
With Marius in command of their camp and supplies the Marsi had to withdraw.
Marius then sent the corpses of Lupus and his officers back to Rome.
Following this, Marius took command of and regrouped Lupus' army.
The Senate then decided to give joint command to Marius and the praetor Quintus Servilius Caepio the Younger.
Marius had expected sole command and he did not get along with Caepio with disastrous results.
After having dealt with a raiding legion of Marsi at Varnia, Caepio attempted to give Marius instructions, but Marius ignored them.
Caepio left on his own and was then obliged to move his legions back towards Caeoli.
Once they reached the Arno at Sublaqueum they were attacked by the Marsi.
Caepio's column perished to the last man.
It is said he was killed by Quintus Poppaedius Silo himself.
Marius now in sole command continued the fight against the Marsi and their allies.
After a lot of maneuvering the Marsi and Marruncini were defeated in a battle where Marius worked in tandem with Lucius Cornelius Sulla, his old subordinate from the Jugurthine and Cimbri wars, together they killed 6,000 rebels, including the Marruncini general Herius Asinus, and captured 7,000.
Marius failed to follow up on this success for unknown reasons (probably because he did not trust his men's morale), he steadfastly refused to engage the enemy.
This led Poppaedius Silo, one of the Marsi generals, to challenge him: 'So if you are such a great general, Marius, why not come down [from your fortifications] and fight it out?'
To this Marius retorted 'Well, if you think you are any good a general, why don't you try to make me?'

By 89 BC Marius had or had been retired from the war.
Either he had withdrawn under the pretext of ill-health because he felt he was being under-appreciated or he was genuinely ill.
There is also the possibility that when his command lapsed at the end of 90 BC the government simply did not renew it or they may have offered him a face-saving deal: retire and claim infirmities.

The Italian war for citizenship was hard-fought.
And in 90 BC, the Assembly carried a law, the lex Julia de civitate latinis et sociis danda to grant citizenship to Italians not yet under arms.
In early 89 BC, with the expansion of the war slowing, the Senate dispatched Lucius Porcius Cato to take over the troops under Marius' command.
Shortly after arriving, he forced Marius to resign his legateship by claiming he was in poor health.

Marius' experience in the conflict brought him few honors, though he served at a senior level and won at least a few victories.
In all likelihood, this experience rekindled his desire for further commands and glory, embarking on a path towards seeking command in the east.
While Marius was away in the east and after he returned, Rome had several years of relative peace. But in 95 BC, Rome passed a decree, the Lex Licinia Mucia, expelling from the city all residents who were not Roman citizens. In 91 BC, Marcus Livius Drusus was elected tribune and proposed a greater division of state lands, the enlargement of the Senate, and a conferral of Roman citizenship upon all freemen of Italy. But after Drusus was assassinated, many of the Italian states then revolted against Rome in the Social War of 91–88 BC, named after the Latin word for ally, socii.
Marius, rather humiliatingly, had to serve as a legate with his nephew, the consul Publius Rutilius Lupus. Lupus died in a Marsic ambush on the River Tolenus. Marius, who was leading another column of men, crossed the river at a different location and captured the Marsic camp. He then marched on the Marsi while they were busy stripping the corpses and dealt with them accordingly. With Marius in command of their camp and supplies the Marsi had to withdraw. Marius then sent the corpses of Lupus and his officers back to Rome. Following this, Marius took command of and regrouped Lupus' army. The Senate then decided to give joint command to Marius and the praetor Quintus Servilius Caepio the Younger. Marius had expected sole command and he did not get along with Caepio with disastrous results. After having dealt with a raiding legion of Marsi at Varnia, Caepio attempted to give Marius instructions, but Marius ignored them. Caepio left on his own and was then obliged to move his legions back towards Caeoli. Once they reached the Arno at Sublaqueum they were attacked by the Marsi. Caepio's column perished to the last man. It is said he was killed by Quintus Poppaedius Silo himself. Marius now in sole command continued the fight against the Marsi and their allies. After a lot of maneuvering the Marsi and Marruncini were defeated in a battle where Marius worked in tandem with Lucius Cornelius Sulla, his old subordinate from the Jugurthine and Cimbri wars, together they killed 6,000 rebels, including the Marruncini general Herius Asinus, and captured 7,000. Marius failed to follow up on this success for unknown reasons (probably because he did not trust his men's morale), he steadfastly refused to engage the enemy. This led Poppaedius Silo, one of the Marsi generals, to challenge him: 'So if you are such a great general, Marius, why not come down [from your fortifications] and fight it out?' To this Marius retorted 'Well, if you think you are any good a general, why don't you try to make me?'
By 89 BC Marius had or had been retired from the war. Either he had withdrawn under the pretext of ill-health because he felt he was being under-appreciated or he was genuinely ill. There is also the possibility that when his command lapsed at the end of 90 BC the government simply did not renew it or they may have offered him a face-saving deal: retire and claim infirmities.
The Italian war for citizenship was hard-fought. And in 90 BC, the Assembly carried a law, the lex Julia de civitate latinis et sociis danda to grant citizenship to Italians not yet under arms. In early 89 BC, with the expansion of the war slowing, the Senate dispatched Lucius Porcius Cato to take over the troops under Marius' command. Shortly after arriving, he forced Marius to resign his legateship by claiming he was in poor health.
Marius' experience in the conflict brought him few honors, though he served at a senior level and won at least a few victories. In all likelihood, this experience rekindled his desire for further commands and glory, embarking on a path towards seeking command in the east.
Gaius Marius