All civilizations have a ‘core state’ (see http://en.wikipedia.org/wiki/The…) except islam, which last relied upon the Turks as the core state. Iran wants to become the core state of islamic civilization, control middle eastern oil, capture the profits from it, and build a military strong enough to ensure it’s centrality, with those profits. If possible, the strategic route to making this come about is to create an alliance, dependency, or at least lack of opposition with Lebanon, Syria, Iraq, Afghanistan and Pakistan, where Pakistan and Iran hold nuclear weapons. That is the Iranian strategic objective.
Whether or not Iraq is a Vassal of Iran is an improper use of language. Iraq is no longer capable of opposing Iranian strategic initiatives, and is subject to iranian political pressure. So it is perhaps better to categorize Iraq as successfully within the sphere of influence of Iran, and therefore contributing to the potential of Iran to become the Core State of Islamic civilization — against the wishes of the southern states.