Peter W. Galbraith in The New York Review of Books:
Treacherous Alliance: The Secret Dealings of Israel, Iran, and the United States
by Trita Parsi.
Iran’s role in Iraq is pervasive, but also subtle. When Iraq drafted its permanent constitution in 2005, the American ambassador energetically engaged in all parts of the process. But behind the scenes, the Iranian ambassador intervened to block provisions that Tehran did not like. As it happened, both the Americans and the Iranians wanted to strengthen Iraq’s central government. While the Bush administration clung to the mirage of a single Iraqi people, Tehran worked to give its proxies, the pro-Iranian Iraqis it supported — by then established as the government of Iraq — as much power as possible. (Thanks to Kurdish obstinacy, neither the US nor Iran succeeded in its goal, but even now both the US and Iran want to see the central government strengthened.)
Since 2005, Iraq’s Shiite-led government has concluded numerous economic, political, and military agreements with Iran. The most important would link the two countries’ strategic oil reserves by building a pipeline from southern Iraq to Iran, while another commits Iran to providing extensive military assistance to the Iraqi government. According to a senior official in Iraq’s Oil Ministry, smugglers divert at least 150,000 barrels of Iraq’s daily oil exports through Iran, a figure that approaches 10 percent of Iraq’s production. Iran has yet to provide the military support it promised to the Iraqi army. With the US supplying 160,000 troops and hundreds of billions of dollars to support a pro-Iranian Iraqi government, Iran has no reason to invest its own resources.
Of all the unintended consequences of the Iraq war, Iran’s strategic victory is the most far-reaching.