The final decades of this era saw a worsening economic situation for many plebeians. The long military campaigns had forced citizens to leave their farms to fight, only to return to farms that had fallen into disrepair. The landed aristocracy began buying bankrupted farms at discounted prices. As commodity prices fell, many farmers could no longer operate their farms at a profit.<49> The result was the ultimate bankruptcy of countless farmers. Masses of unemployed plebeians soon began to flood into Rome, and thus into the ranks of the legislative assemblies. Their economic state usually led them to vote for the candidate who offered the most for them.
The prior era saw great military successes, and great economic failures. The patriotism of the plebeians had kept them from seeking any new reforms. Now, the military situation had stabilised, and fewer soldiers were needed. This, in conjunction with the new slaves that were being imported from abroad, inflamed the unemployment situation further. The flood of unemployed citizens to Rome had made the assemblies quite populist.
Tiberius Gracchus was elected tribune in 133 BC. He attempted to enact a law which would have limited the amount of land that any individual could own. The aristocrats, who stood to lose an enormous amount of money, were bitterly opposed to this proposal.
Then he was assassinated.
http://en.wikipedia.org/wiki/Roman_RepublicForeign dominance led to internal strife. Senators became rich at the provinces' expense, but soldiers, who were mostly small-scale farmers, were away from home longer and could not keep up their land, and the increased reliance on foreign slaves and the growth of latifundia reduced the availability of paid work.
Income from war booty, mercantilism in the new provinces, and tax farming created new economic opportunities for the wealthy, forming a new class of merchants, the equestrians.The lex Claudia forbade members of the Senate from engaging in commerce, so while the equestrians could theoretically join the Senate, they were severely restricted in political power. The Senate squabbled perpetually, repeatedly blocking important land reforms and refusing to give the equestrian class a larger say in the government.
Violent gangs of the urban unemployed, controlled by rival Senators, intimidated the electorate through violence. The situation came to a head in the late 2nd century BC under the Gracchi brothers, a pair of tribunes who attempted to pass land reform legislation that would redistribute the major patrician landholdings among the plebeians. Both brothers were killed, but the Senate passed some of their reforms in trying to placate the growing unrest of the plebeian and equestrian classes.
The denial of Roman citizenship to allied Italian cities led to the Social War of 91–88 BC. The military reforms of Gaius Marius resulted in soldiers often having more loyalty to their commander than to the city, and a powerful general could hold the city and Senate ransom.
http://en.wikipedia.org/wiki/Ancient_Rome