When did Roman citizenship extend to all of Italy?

Roman citizenship was extended to the inhabitants of Italy primarily as a result of the Social War (90–89 BCE).12

During this conflict, Rome sought to pacify its rebelling Italian allies (socii) by passing legislation, such as the law introduced by the consul Lucius Julius Caesar, which granted citizenship to those who had not participated in the revolt or who were willing to lay down their arms. By the end of the war, full citizenship had been conferred upon all of Italy south of the Po River, effectively unifying the region into a single nation.132