From the very beginning of the reign of Nero (AD 54), and actually stretching from the later reign of Claudius, the political situation in the east was beginning to show signs of impending danger. Vologeses, the King of Parthia, had begun interfering with Roman interests in Armenia, although the region was long contested by both great powers, it still retained some level of independence. In the same year as the death of Claudius, Vologeses installed his own brother, Tiridates as King of Armenia, in favor of the Roman client who already ruled. This violation of law and peace (Rome held the right of determining Armenia's governmental authority since the time of Augustus) would eventually lead to war, but the Romans were ill prepared to conduct a major campaign. Needing an experienced general to make those preparations, Nero (and Seneca who introduced a decidedly more aggressive eastern policy than that of Claudius) turned to Cnaeus Domitius Corbulo, an honored commander from the Germanic borders under the reign of the previous emperor.
Upon Corbulo's arrival his assessments prevented immediate action against Armenia or Parthia, and he set about training and levying new recruits. Over the course of the next few years (including varying degrees of both military and political jockeying) Corbulo laid the groundwork to re-establish Roman authority. By late AD 57 he was finally prepared and an 11th hour negotiation attempt that ended in failure left the door open for hostilities to commence. An initial attack by Tiridates was initially successful but not enough to have any lasting effect and he retreated into the deeper desert of Armenia to avoid direct conflict. Corbulo followed but was unable to bring Tiridates to battle and broke off direct pursuit in order to focus on the Armenian capitals. First Artaxata was captured and sacked and by the end of AD 59 Tigranocerta surrendered to the advancing Romans without a fight. The following year, a Parthian army under Tiridates' command was repulsed leaving Corbulo and the Romans to claim victory in the overall affair. Nero appointed Tigranes (a great-grandson of Herod the Great) as the new pro-Roman King, and Corbulo was appointed governor of Syria as a reward.
All was not over, however. In AD 61, Tigranes continued the fight against Parthian influences, eventually forcing the Romans to return to his aid. Corbulo sent two legions directly into Armenia while three more were amassed on the border with Parthia as a warning. This forced a temporary truce while the Parthia King Vologeses send an embassy to Rome to conclude the matter completely. However, not unexpectedly, negotiations broke down and by AD 62 the war was back on.
The governor of Cappadocia, Lucius Caesennius Paetus, led the Roman side in Armenia for the next season, while Corbulo decided to cross the Euphrates and take the fight directly to Parthia. Though the plan had merit, neither Vologeses nor Paetus complied. Out of the reach of Corbulo's assistance, Vologeses besieged the poorly prepared Paetus forcing him to surrender. Though Corbulo was marching to his aid, Paetus' treaty forced Roman withdrawal while another round of 'executive' negotiations would take place between Nero and Vologeses. These again broke down and by AD 63 both sides were back at it.
In the new campaign year Corbulo was given supreme authority (maius imperium) and prepared an invasion using his four best legions. While the Parthians understood that victory for their side was becoming unreachable Corbulo understood that a Roman victory would be terribly costly. Before his considerable force could be brought to bear the two sides entered a final negotiation where nearly 10 years of stalemate would end at almost exactly the same position as where it started. The Parthians conceded that the Romans had overall authority to name the Armenian King, and Tiridates (the Parthian choice) was forced to lay down his crown. However, in an entirely ceremonial gesture, Tiridates was brought to Rome where Nero would return it himself thereby proving complete Roman authority in the matter.
Despite the fact that very little had occurred in the entire series of campaigns (other than death and bloodshed) without any change in the result, Roman propaganda staged this as a great victory. Nero was in serious political jeopardy by this point (it was AD 66 before Tigranes showed up in Rome) and he needed a great victory to boost his image. A grand celebration took place granting Corbulo full military honors and the doors to the Temple of Janus were shut (symbolically meaning that there was peace throughout the Roman world). However in an ironic twist of fate and as an indication of the mass paranoia that followed Nero late into his reign, Corbulo was forced to commit suicide just a year later, in AD 67. Corbulo's death, along with several other popular generals of the time, would help usher in the massive military revolt that would eventually force Nero's own suicide. Corbulo's family would remain a part of Imperial intrigue of its own merit though. His daughter Domitia Longina would eventually be married to the emperor Domitian and is suspected of likely involvement in his assassination.