The Pompei-Caesar civil war was violent on a scale not previously experienced by Rome. It was bad for the Ancient Mediterranean world in general. The war disrupted its agricultural bases and was economically wasteful, in addition to bringing political uncertainty, as the petty potentates in client relations to Rome were not sure with whom to adhere, since they were uncertain who would be victorious. Additionally, much life was lost, with the elite of Rome and the outlying Italian cities being prominently represented among the victims. In 47 BCE, Caesar returned from the East, and was publicly pardoned by the Senate. Pompeii's supporters renewed the Senate with their own numbers, after which Caesar left to confront North African rebels under Q. Metullus Scipio. Arriving in the winter of 47-46, he only had half an army, and waited until the spring before destroying the Pompeiian-supported rebels at Thapsus. His forces massacred the rebels. The Rome Senate then accorded him the power of Dictator for ten years, allowing him as well a four-fold triumph: victories over the last ten years were celebrated, including Gaul, Egypt, Pontus, and Africa. Just after this he defeated a further rebellion under Pompei's son, Sextus Pompei, in Iberia at Munda. This was the last civil war battle in Caesar's time. His status as Dictator provided him commands of the army and provinces; financial control, foreign policy decisions, as well as tribunal veto power over judicial decisions and legislation. Basically, he had the untouchable power to run government. In 47 BCE he renewed the Senate, raising its numbers to 900, appointing great numbers of his supporters. These included Italian town equites, certain freedmen, and ex-centurions.
Caesar also promulgated several points of practical legislation: 1) He changed the calendar, reforming it into the Julian calendar; 2) he permitted the urban tribunes to attack street gangs. Collegia were made illegal, but exempted Jews due to their assistance to him when he was in Alexandria; 3) in urban courts, the jury was divided equally between equites and senators; 4) he began to break the barriers in the relations between Rome and the provinces. Caesar was liberal with grants of Roman citizenship, bestowing it of Cisalpine Gaul, the provincial urban centers, as well as certain individuals, and elevated other provincial cities to Latin citizen rights status. It was the first wholesale extension of citizenship. As well, he began appointing outsiders to the Senate; 5) He planned Caesarian colonies, or the roots of cities in less Romanized areas such as Southern Gaul, Iberia, Africa, and Asia Minor. In 44 BCE there were 35 legions under arms. Caesar proposed to settle de-mobilized soldiers and veterans in these cities as well as Rome's urban unemployed; 6) Caesar tried to change the method of provincial tribute. It had been based on tithe in kind, but he wanted to shift it to a fixed land tax.
In 44 BCE, Caesar relied on his senatorial supporters to elect him Dictator for Life—dictator perpetuus. He went on to plan an attack on Parthia, the Persian state in the far eastern reaches of Roman territories. However, on March 15, 44—the Ides of March—sixty senators conspired to murder him, on the steps of the Senate House named for Pompei. Cassius, along with the scholarly, philosophical M. Brutus, were the titular ringleaders of a group including some older senators who had opposed Caesar all along, as well as some of his erstwhile supporters who objected to his deprivation of certain Rome aristocrats of jobs, as well as his growing autocracy. While the conspirators fled Rome, and later Italy, Caesar's party—the factio—was now left in confusion. One of them, the competent general Marcus Antonius who was Consul in 44, came to temporary leadership of the group, declaring an amnesty to the conspirators. He also declared that Caesar's legislative initiatives would stand.
At Caesar's death, the first thing Mark Antony did was to go to Caesar's residence, take all the material wealth he could, as well as his will. Another prominent member of Caesar's factio was M. Aemilius Lepidus, who was about to become governor of Narbonnese Gaul and brought his seven legions to Rome in order to subdue the capital if need be. Mark Antony restrained him, and started to move towards predominance. There was one other player, however. Caesar's will had (allegedly) listed C. Octavian as heir to his personal fortune and social position. Octavian's grandfather had married a sister of Caesar; Octavian was thus Caesar's grand nephew. At the age of eighteen, he had (somewhat unusually) just passed from equestrian to senatorial rank. He was currently out of Italy, doing military training, and returned to Rome as soon as he heard of Caesar's death, changing his name to C. Julius Caesar Octavianus. Passing through Italy, he had begun to collect supporters among veterans from Caesar's legions. He immediately found that Mark Antony had depleted Caesar's personal as well as state funds. Octavian still needed an army. He prevailed upon the Senate to provide him with the proconsular command in Cisalpine Gaul; however Decimus Brutus—related to the co-conspirator—was already on the ground there. It was around this time that the orator-politician returned to Rome and delivered his series of addresses entitled the Philippics, in which he repeatedly condemned Mark Antony as an aspiring despot. At this time those senators who had supported the assassination allied with Octavian as a brake on growing tyranny, granting him the propraetorship in Cisalpine Gaul, along with two legions. Around this time, D. Brutus defeated the besieging Mark Antony at Mutina. In this, D. Brutus was assisted by Octavian, who had linked up with Senate-dispatched relief forces. M. Antony was forced to retreat to Italy, yet ultimately, his forces overpowered those of Brutus. At this point, Octavian began to break with the Senate. The latter gave fellow conspirators M. Brutus and Cassius proconsulships in Macedonia and Syria, respectively. The also Senate did not appropriate the funds for Octavian to pay his soldiers. In July 43, Octavian forced the issue by demanding one of the vacant consulships. The Senate refused, giving him the praetorship instead. Octavian then marched on Rome with eight legions. Through cultivating the masses—plebs—and raising a veteran-based army, as well as through the support of military friends such as M.V. Agrippa and C. Maecenas, he was able to engineer his election as consul. At this point, Lepidus declared for Antony, and senatorial control of the western provinces collapsed. Octavian then rescinded the amnesty for Caesar's murderers, and hastened to attempt an agreement with Antony and Lepidus. The three met in Bononia (near Barcelona) and negotiated the Second Triumvirate. Later written into law at Rome through the tribune Titius, it was a three-man dictatorship able to pass laws, appoint all higher magistrates, conscript limitless numbers of soldiers, tax the populace, and prosecute military actions. This lex Titia has been called the definitive end of the Roman Republic. The triumvirs then launched the proscriptions against the anti-Faction camp. 300 senators and 2,000 equites were massacred judicially, including Cicero. Their properties were confiscated, to pay off soldiers and factio supporters.
The next challenge for the Second Triumvirate were Cassius and Brutus. By 43, the two had taken over all of Asia Minor as well as other Eastern provinces, and had gotten the allegiances of lesser potentates, such as Cleopatra and were moving into Macedonia. Antony and Octavian combined forces and met their opponents at Philippi. In the first battle, Octavian was initially bested by Brutus, but Antony's troop defeated Cassius, who then committed suicide. Two weeks later, the factio ended all hopes of the conspirators, by defeating Brutus, who took his own life as well. The victors went on the divide Roman lands between them. Earlier, Lepidus and M. Antony had received most of Gaul and Spain, while Octavian was awarded Italian Islands and Africa, with Italy being shared. After Philippi, however, Antony seemed ascendant. He received most regions, while Lepidus was about of favor. To Octavian fell the duty of settling about 100,000 soldiers of the conspirators; disbanded legions in Italy and southern Gaul, while Mark Antony went off to discover glory in the East by fighting Parthia. In settling his troops during 42-41, Octavian incurred the displeasure of Italian aristocrats whose lands were taken. M. Antony's brother L. Antonius, as well as Mark's wife Fulvia galvanized armed opposition to Octavian, with Mark's support. Octavian and his colleague Agrippa defeated them at Perusia, with the aide of troops from Gaul, who saw him as Caesar's heir. in de facto terms, Octavian had thus taken control of the western Roman regions.
At this point (40 BCE) Antony returned from desultory and costly wars in the East. Octavian's commander at Brundisium refused him entry into Italy. At this point, Octavian's ally C.C. Maecenas interceded to produce a new triumviral understanding. Antony kept control of eastern provinces, while ceding Spain, Gaul, and Illycricum to Octavian. Lepidus received Africa. The deal was sealed when Octavian's sister, Octavia, married Mark Antony. Shortly after, a problem emerged in Italy. Sextus Pompei controlled Sicily, Corsica, and Sardinia, with a small republican army and a fleet. He acted as a pirate, disrupting trade and communication for the populations of the mainland. In 39, he stepped up his campaign, at which time Octavian decided to destroy him. He had no fleet though, and received one from Mark Antony on condition that he subsequently transfer four of his legions to the East. Under Agrippa's command, Octavian's forces finally defeated Sextus at Naulochus. His twenty-three legions surrendered to Lepidus, who then requested Octavian's evacuation of the area. OCtavian refused, whereupon Sextus' old forces transferred their allegiance to Octavian, out of war weariness. At this point, Octavian had the most forces and least liabilities of the three triumvirate members. Lepidus retired peacefully. For the next five years (38-33), Octavian remained mostly in the West, as the restorer of peace to the Roman world. Mark Antony was still off in the East campaigning.