Man is this like a school problem or something? :) lol..there are several reasons but basically it boils down to the problem of the land-owning farmer of the early Res Publica not being able to maintian his indpendent land with the rise of the latifunda and corporate-owned industrial farming. Hannibal also had alot to do with it; throughout the later 200s BCE much farmland was destroyed in Italia, many farmers were made soldiers, long periods of fighting in Hispania for instnace kept them away from their lands that were gobbled up by hungry corporations, making them paupers when they returned from years of war. The government began to subsidize the poor, and veterans were implanted in colonia across the realm,etc.

There was also an ever-widening gulf between rich and poor in Rome. With the influx of treasure and taxes from Rome's new dominions, Senators became wealthier by the year--new luxuries unknown in older Rome were becoming popular by this time, with pleasure villas being erected up and down the Campanian coast, etc.