Have another civil war, why don't ya?
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On one side was Gaius Cornelius Homullus, who was popular with the Senate and the central regions of the Empire, such as Italy, Greece, Anatolia, Syria, and Egypt. Opposing him was Secundus Amaticus Darius, who was popular with the eastern areas, such as Persia (his birthplace) and Mesopotamia, as well as in Gaul and Britannia. This civil war would drag out for much longer than the previous war, as neither side could gain an advantage over the other.
AD 170 would see Homullus winning at the battle of Lutetia. In 171, Darius would claim victory at Mediolanum, while Homullus would win at Lugdunum and Sirmium. During 172, Darius would win pyrrhic victories at Thessalonica, Ancryra,and Palmrya.
In that same year, the Parthian provinces would rebel, creating a pocket empire out of Parthia Superior and Inferior, Margiana, and Aria. Meanwhile, the Venedae began to raid into Carpia, Costobocia, and Roxolania. Both Darius and Homullus were too focused on defeating each other to give any time to either of these threats.
173 would see no major battles, except for a naval engagement at Alexandria, which both sides claimed as a victory (Darius destroyed almost all of Homullus' navy, but was prevented from making a landing and was turned away). The Parthians were sending diplomatic feelers to see if they could profit from allying with either general, though this lead to nothing. The Venedae continued to raid unchallenged into Roman territory, until the Gothonians stepped in.
Seeing an opportunity to expand, Atreus II attacked the Venedae, forcing them on the defensive. Though the incursions into Roman territory would continue into 174, this gave the neutral Roman garrisons time to recover and put up some semblance of defense.
The civil war would continue on through 175, with engagements at Cyrene, Seleucia Magna, Ecbatana, and Carthago. The Gothonians continued to press the Venedae and had already defeated most of the northern tribes.
The war finally ended in AD 176 when Homullus died of malaria. His forces, who were weary of the fighting, surrendered to Darius soon after, leaving him to become Emperor.
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Thoughts? Comments? Money?