The Roman Republic lasted for roughly five centuries. It was under the Republic that Rome evolved from a single town to the heart of an enormous empire. Despite the evident success of the Republican system, however, there were inexorable problems that plagued the Republic throughout its history, most evidently the problem of wealth and power. Roman citizens were, by law, supposed to have a stake in the Republic. They took pride in who they were and it was the common patriotic desire to fight and expand the Republic among the citizen-soldiers of the Republic that created, at least in part, such an effective army. At the same time, the vast amount of wealth captured in the military campaigns was frequently siphoned off by elites, who found ways to seize large portions of land and loot with each campaign. By around 100 BCE even the existence of the Plebeian Assembly did almost nothing to mitigate the effect of the debt and poverty that afflicted so many Romans thanks to the power of the clientage networks overseen by powerful noble patrons.
The key factor behind the political stability of the Republic up until the aftermath of the Punic Wars was that there had never been open fighting between elite Romans in the name of political power. In a sense, Roman expansion (and especially the brutal wars against Carthage) had united the Romans; despite their constant political battles within the assemblies and the senate, it had never come to actual bloodshed. Likewise, a very strong component of Romanitas was the idea that political arguments were to be settled with debate and votes, not clubs and knives. Both that unity and that emphasis on peaceful conflict resolution within the Roman state itself began to crumble after the sack of Carthage.
The first in the step toward violent revolution in the Republic was the work of the Gracchus brothers – remembered historically as the Gracchi (i.e. “Gracchi” is the plural of “Gracchus”). The older of the two was Tiberius Gracchus, a rich but reform-minded politician. Gracchus, among others, was worried that the free, farm-owning common Roman would go extinct if the current trend of rich landowners seizing farms and replacing farmers with slaves continued. Without those commoners, Rome's armies would be drastically weakened. Thus, he managed to pass a bill through the Centuriate Assembly that would limit the amount of land a single man could own, distributing the excess to the poor. The Senate was horrified and fought bitterly to reverse the bill. Tiberius ran for a second term as tribune, something no one had ever done up to that point, and a group of senators clubbed him to death in 133 BCE.
Tiberius's brother Gaius Gracchus took up the cause, also becoming tribune. He attacked corruption in the provinces, allying himself with the equestrian class and allowing equestrians to serve on juries that tried corruption cases. He also tried to speed up land redistribution. His most radical move was to try to extend full citizenship to all of the Rome's Italian subjects, which would have effectively transformed the Roman Republic into the Italian Republic. Here, he lost even the support of his former allies in Rome, and he killed himself in 121 BCE rather than be murdered by another gang of killers sent by senators.
The reforms of the Gracchi were temporarily successful: even though they were both killed, the Gracchi’s central effort to redistribute land was largely successful – a land commission created by Tiberius remained intact until 118 BCE, by which time it had redistributed huge tracts of land held illegally by the rich. Despite their vociferous opposition, the rich did not suffer much, since the lands in question were “public lands” largely left in the aftermath of the Second Punic War, and normal farmers did enjoy benefits. Likewise, despite Gaius’s death, the Republic eventually granted citizenship to all Italians in 84 BCE, after being forced to put down a revolt in Italy. Instead, the historical importance of the Gracchi was less in their reforms and more in the manner of their deaths - for the first time, major Roman politicians had simply been murdered (or killed themselves rather than be murdered) for their politics. It became increasingly obvious that true power was shifting away from rhetoric and toward military might.
A contemporary of the Gracchi, a general named Gaius Marius, took further steps that eroded the traditional Republican system. Marius combined political savvy with effective military leadership. Marius was both a consul (elected an unprecedented seven times) and a general, and he used his power to eliminate the property requirement for membership in the army. This allowed the poor to join the army in return for nothing more than an oath of loyalty, one they swore to their general rather than to the Republic. Marius was popular with Roman commoners because he won consistent victories against enemies in both Africa and Germany, and he distributed land and farms to his poor soldiers. This made him a people's hero, and it terrified the nobility in Rome because he was able to bypass the usual Roman political machine and simply pay for his wars himself. His decision to eliminate the property requirement meant that his troops were totally dependent on their general for loot and land distribution after campaigns, increasing their loyalty to him, but undermining their allegiance to the Republic.
Marius was the first Roman general to draw from the vast pool of poor male citizens in the city of Rome itself, which by this time had a population of around a million people. Marius's recruiters offered good pay and equipment to any Roman man willing to join Marius's army, and as a result Marius became a popular hero among the poor in Rome, much to the horror of the Roman elite, who feared the "mob" of poor citizens.
A general named Sulla followed in Marius's footsteps by recruiting soldiers directly and using his military power to bypass the government. In the aftermath of the Italian revolt of 88 - 84 BCE, the Assembly took Sulla’s command of Roman legions fighting the Parthians away and gave it to Marius in return for Marius’s support in enfranchising the people of the Italian cities. Sulla promptly marched on Rome with his army, forcing Marius to flee. Soon, however, Sulla left Rome to command legions against the army of the anti-Roman king Mithridates in the east. Marius promptly attacked with an army of his own, seizing Rome and murdering various supporters of Sulla. Marius himself soon died (of old age), but his followers remained united in an anti-Sulla coalition under a friend of Marius, Cinna.
After defeating Mithridates, Sulla returned and a full-scale civil war shook Rome in 83 – 82 BCE. It was horrendously bloody, with some 300,000 men joining the fighting and many thousands killed. After Sulla’s ultimate victory he had thousands of Marius’s supporters executed. In 81 BCE, Sulla was named dictator; he greatly strengthened the power of the Senate at the expense of the Plebeian Assembly, had his enemies in Rome murdered and their property seized, then retired to a life of debauchery in his private estate (and soon died from a disease he contracted). The problem for the Republic was that, even though Sulla ultimately proved that he was loyal to Republican institutions, other generals might not be in the future. Sulla could have simply held onto power indefinitely thanks to the personal loyalty of his troops