By Kamran Bokhari
Summary Though Iran is heavily involved in Syria, Iraq will always be the most critical foreign policy arena for the Islamic republic. Even before the Islamic State captured Mosul in the summer of 2014, Tehran had to exert a great deal of effort to ensure that its Shiite allies were able to dominate the post-Baathist Iraqi government. The IS takeover of most of the Sunni areas of Iraq created a major security situation, which compounded the political problems that the Iranians faced before then. Even in the event of the neutralization of IS in Iraq, Iran will be struggling to manage its western neighbor because the Iraqi Shiite politicians remain factionalized.
For Iran, the 2003 U.S. invasion of Iraq was a godsend. Saddam Hussein and his Baathist regime had waged an eight-year war (1980-1988) against the then-nascent Islamic republic that left nearly a million Iranians dead and cost the country hundreds of billions of dollars. But Tehran was not only pleased a