From what I understand, Mesopotamia was the economic heartland of the Persian Empire and its various incarnations ( e.g Parthians, Sassanids) since it the area around the Eufrates and Tigris rivers was so fertile, explaining why so many cities were located either in it or near it such as Babylon, Akkad, Susa, Assur, Niniveh, Ctesiphon and Seleucia.
In the early 2nd century AD the Romans under Trajan conquered it, severely weakening the Parthian Empire. And the Roman Empire looked like on the map in the link below which was its greatest extent:
http://en.wikipedia.org/wiki/File:RomanEmpire_117.svg
IOTL the Romans left it because they felt they were overextended and Trajan felt too old to follow in the footsteps of Alexander the Great. Suppose the Romans somehow keep Mesopotamia and establish a border on the Zagros mountains after some more campaigning, crippling the Parthians and setting them up as puppets in what is now Iran. This relieves pressure on the eastern border immensely.
How does this effect the Romans in centuries to come and the Byzantines if the west still falls in spite of butterflies?
Note: my knowledge on the time period is limited so if I'm off-track, please don't keep it to yourself.
EDIT: lets say Caledonia is also conquered due to butterflies (and perhaps Hibernia), eliminating another border for the Romans to guard.
In the early 2nd century AD the Romans under Trajan conquered it, severely weakening the Parthian Empire. And the Roman Empire looked like on the map in the link below which was its greatest extent:
http://en.wikipedia.org/wiki/File:RomanEmpire_117.svg
IOTL the Romans left it because they felt they were overextended and Trajan felt too old to follow in the footsteps of Alexander the Great. Suppose the Romans somehow keep Mesopotamia and establish a border on the Zagros mountains after some more campaigning, crippling the Parthians and setting them up as puppets in what is now Iran. This relieves pressure on the eastern border immensely.
How does this effect the Romans in centuries to come and the Byzantines if the west still falls in spite of butterflies?
Note: my knowledge on the time period is limited so if I'm off-track, please don't keep it to yourself.
EDIT: lets say Caledonia is also conquered due to butterflies (and perhaps Hibernia), eliminating another border for the Romans to guard.