Scholar/diplomat Dore Gold observes:

[T]here is a need to recognize that this is a regional war. Iran is seeking to dominate Iraq, particularly its southern Shia areas — the provinces where British troops are deployed — and hopes to encircle both Israel and the Sunni heartland of the Arab world. Syria is Iran’s main Arab ally in this effort. There is no question that Iran’s main aim is to dominate the oil-producing areas by agitating the Shia populations of Kuwait, Bahrain, and the eastern provinces of Saudi Arabia.

More here.