Rome's military and diplomatic successes around the Mediterranean resulted in unforeseen economic and political pressures on the state. While factional strife had always been part of Roman political life, the stakes were now far higher; a corrupt provincial governor could acquire unbelievable wealth; a successful military commander needed only the support of his legions to rule vast territories. Starting with the Punic Wars, the Roman economy began to change, concentrating wealth in the hands of a few powerful clans and causing political tension within Rome.
Much of the newly conquered territories were seized by rich and powerful families. Additionally, as only men who could provide their own arms were eligible to serve in the Legions, the majority of Roman troops came from the middle class land holders who theoretically would be fighting to defend their own lands. With military campaigns now lasting years rather than just a few months, soldiers could not return to work their farms. With their holdings lying fallow, their families quickly fell into debt, and their lands were lost to creditors- typically wealthy landholders who consolidated these properties into vast latifundia. Formerly middle-class soldiers would return from years of campaigning to find themselves landless, unable to support their families, and ironically, unemployable because the successes of the Legions made slaves a much cheaper source of labor.
By 133 BC the economic imbalance was too acute to ignore, but the wealthy patricians and old families in the Senate had a vested interest in preserving the status quo. It seemed that a land reform through the traditional channels was an unlikely prospect. In 133 BC, a tribune, Tiberius Sempronius Gracchus, tried to introduce land reform to redistribute "publicly held land" to the now landless returning soldiers. He proposed the enforcement of a Roman law, which had mostly been ignored, which limited the use of public lands. While "public lands" were technically state owned, such land was often used by wealthy landholders, many of them Senators. Under the enforcement of this law many of them would lose property.
As it seemed unlikely that the Senate would agree to enforce the law, Tiberius bypassed the Senate entirely, and tried to pass his reform through the Plebeian Assembly as a plebiscite, using the legal principle of Lex Hortensia. While technically legal, this was a violation of political custom, and outraged many patricians. The Senate blocked Tiberius by bribing his fellow tribune to veto the bill. Tiberius then passed a bill to depose his colleague from office, violating the principle of collegiality. With the veto withdrawn, the land reform passed. An incensed Senate refused to fund the land commission. Tiberius used the plebeian assembly to divert funds from the income of Pergamon to fund the commission, challenging Senate control of state finances and foreign policy. When it became clear that Tiberius did not have enough time to finish his land reforms, even with political and economic backing, he announced that he would run again for the tribunate, violating annuality. This was the last straw for the patricians, who, fearing that Tiberius was setting himself up as a tyrant, responded by slaughtering Tiberius and 300 of his followers in the streets of Rome.
Tiberius' younger brother Gaius Sempronius Gracchus attempted to continue political reforms using similar tactics almost ten years later. He seems to have been more of a demagogue who attempted to pass a slew of popular laws to gain popular support rather than to be a political reformer with a specific agenda like his brother. He was neither as successful, nor as popular, as his elder brother, but he managed to create many political enemies. Escalating political tensions finally exploded once again in violence on the Capitoline Hill, where Gaius Gracchus and 3,000 of his followers were killed.
Whatever their intentions, the political careers of the Gracchi brothers had broken the political traditions of Rome, and introduced mob violence as a tool of Roman political life. It was a change that the Republic would not recover from.
Tiberius and Gaius Gracchus attempted land reform. They confiscated land from the wealthy classes and distributed it among the proletarii. They were both assassinated. This was the first bloodshed in Roman domestic politics.