I can chip in.

Pre-Islam: Arabs were split into two spheres of influence. The Persians had supported the man who eventually became king in Iraq and the Romans had the Ghasani people in The Levant.

Both were Arabs, ruling on behalf of their “masters” and even took their religion.

At some point before the start of Islam, within 40- 50 by most estimates. the man in Iraq disobeyed the Persian Emperor, Khosro the Second, and a long chain if events kicked out culminating in the Battle of Dhi Qar. This battle is significant as it marks the first Arab victory over the Persians, ever. The mighty Persian Army can be defeated.

Jump to Roman Persian war you are asking about: that the war was big news at the time.

There is a chapter in the Quran called “Al-Rum” (The Romans / or Rome)

The pagans supported the Persians, the Muslims supported the Christian Romans, the chapter starts off announcing that the Romans have lost a major battle, at a nearby location (Jordan), but prophesies that the Romans will ultimately win the war, which they did.

Ultimately the Muslims focused their efforts on Persia and were more successful over there due to the military differences between Persia and Rome.

The differences between Levant and Iraq continued even after Muslim conquest and competition between the two was fierce; the Muslim Capital moved from Levant to Iraq at some point.