Seleucid Option
Another possibility is that the Romans treated the Seleucid Empire better during the period of 134 BC. You know, say, 'hey, we are not your best friends, but we would like a stable border buffer state with you' and wait till they need more help, at a price. Eventually, like Anatolia, Roman would eventually inherit, when the time was ripe, more like happened in OTL Egypt. The constant threat of the Parthnians would help ensure a grateful population, with occasional bloody pillages to enforce the point. Taxes should be low to further the support of the locals, as unlike Egypt this is no breadbasket for Rome (transportation alone would be a killer with lack of sea routes).
A telling quote confirms what I had read beforehand, that the Romans made a big mistake playing politics, as the Parthnians and their successors gave themselves and the later Byzantines no end of trouble.
The Islamic conquest was one of fierce religious intensity. One does not expect such from a large, old bureaucratic state, nor should one from a large, old corporation.
"and Roman intervention was an ever-present threat." Which goes to show they were trying to repeat the process that gained them Asia Minor Anatolia. Unfortunately, Israel and the Parthnians were eventual big trouble for that.
http://en.wikipedia.org/wiki/Seleucid_Empire#Collapse_.28100.E2.80.9363_BC.29
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Demetrius Nicator's brother,
Antiochus VII Sidetes, took the throne after his brother's capture. He faced the titanic chore of restoring a rapidly crumbling empire; one facing threats on multiple fronts. Hard-won control of
Coele-Syria was threatened by the Jewish Maccabee rebels. Once-vassal dynasties in Armenia, Cappadocia, and Pontus were threatening Syria and northern
Mesopotamia; the nomadic Parthians, brilliantly led by
Mithridates I of Parthia had overrun uppland Media (home of the famed
Nisean horse herd); and Roman intervention was an ever-present threat.
Sidetes managed to bring the Maccadees to heal; frighten the Anatolian dynasts into a temporary submission; and then, in 133, turned east with the full might of the Royal Army (supported by a body of Jews under the Maccabee prince, John Hyrcanus) to drive back the Parthians.
Sidetes' campaign initially met with spectacular success, recapturing Mesopotamia, Babylonia and Media; defeating and slaying the Parthian Satrap of
Seleucia-on-Tigris in personal combat. In the winter of 130/129 BC, his army was scattered in winter quarters throughout Media and Persis when the Parthian king,
Phraates II, counter-attacked. Moving to intercept the Parthians with only the troops at his immediate disposal, he was ambushed and killed. Antiochus Sidetes is sometimes called the last great Seleucid king.
After the death of Antiochus VII Sidetes, all of the recovered eastern territories were recaptured by the Parthians. The Maccabees again rebelled, and civil war soon tore the empire to pieces. And the Armenians began to encroach on Syria from the north.