US afraid of Shias taking control of oil

With the announcement of in excess of 20,000 more US troops being deployed in Iraq, it is now more pertinent than ever to accept the real reason for the war in Iraq: control of Iraqi oil reserves. Without accepting this, talk of a withdrawal of troops from Iraq or an end to the use of Shannon Airport is pointless. The reason for this is that the United States government will not allow a Shia-led government to rule in Iraq without their (US) interference. What would a Shia-led government in control of its own resources in Iraq do?