Background to War
The Parthian Empire and the Roman Empire had been rivals in the world for some time before the start of this War. The Parthians who inherited their Empire from the Persians lived in modern day Iran mainly but extended to OTL Iraq and as far as Afghanistan. The Roman Empire was led by the Emperor Marcus Aurelius who was assisted by the very powerful and famous General, Carolus. The Emperor Marcus Aurelius was not intent of pursuing war with these people but they began to act more hostile against the Romans ever since the Emperor Vologases I of Parthia came to power. Vologases and the King of Armenia funded raids and other border attacks on the Romans which eventually culminated in a large, full-scale siege of the city of Damascus in Syria.
The Battle of ArmeniaThe Armenians were allies of both the Roman Empire and the Parthians. However, despite their peace with these powers the Parthians were their clear favorite. The Parthians were backing the Armenians in their raids and attacks on their border with the Roman Empire. Eventually the city of Damascus in Syria was attacked and the Romans learned that the Armenians and the Parthians had conspired against them. Marcus Aurelius left behind any pretense of keeping the Armenians as Allies and began to attack them. The Battle of Artashat, which was the Capital of Armenia, resulted in the domination of the Armenian nobles by the Roman Legions. The popular support for the end of the tyranny which the Armenian Kings had been ruling with was also insurance of their support in this quick campaign on their way into Parthia.
The Conquest of Parthia
Parthia, being the orchestrator of the attacks on the borders of the Roman Empire, was the area that Marcus Aurelius and Carolus wanted to focus their energy. When they arrived in the capital of Ctesiphon they burned it to the ground and almost all of the soldiers in the Parthian Army were wiped away. Emperor Marcus Aurelius and General Carolus built up new cities and incorporated the Satrapies of the Parthian Empire as new Provinces. The Provinces of Assyria, Babylonia, Arabia, Arachosia, Bactria, Carmenia, Chrasmia, Elegabatia, Margiana, Pasargadia were new to the Roman hegemony. The leaders of these areas had grown disconnected with the government in Ctespihon and they joined with the Romans very well. Satraps became Governors and the central government fell apart. Now the Emperor and the legions had to move back to Rome.
The Crimean War
The Crimeans were a group of tribes actually known as Bulgars and other names. The adopted son of Marcus Aurelius, named Commodus, actually attacked the Crimean tribes in order to get them to attack the returning troops of his father. This was actually done because Carolus was becoming Marcus's favorite and was clearly going to inherit the powers that Commodus expected to gain after his father's death. The start of this battle was done after the legions of Rome were ready to return to Western Europe, however, their Emperor knew that he could not allow a rogue tribe to lay across the important trade routes of the Pantus Euxenos (Black Sea).
Nearly half of the legions that Marcus Aurelius brought with him were now dead but the tribesmen were no match and almost no casualties resulted in this battle. However in the conquest of the city of Simpheropolis (Simforopol), largest on the island of Crimea, the Emperor Marcus Aurelius died on October 21 934 (181 AD). At this time the Bulgars that were captured gave up the knowledge they had to Carolus. Carolus learned of the treachery of Commodus and returned to punish him as he saw fit. Crimea also became occupied and the Bulgars left were subjugated. Commodus was defeated and his name became a pejorative in the Roman Empire. Carolus succeeded Marcus Aurelius as Emperor, which many later claimed was Marcus's will but no records exist to attest to this.