Iran , already deeply mired in Syria’s civil war, now finds itself center stage in a fight against Sunni militants threatening to topple its most important regional partner in Iraq . Iran is pledging to defend Shiite shrines in Iraq and help Prime Minister Nouri al-Maliki defeat an al-Qaeda breakaway group that has routed his northern army. More than 130 members of Iran’s Revolutionary Guards entered Iraq’s eastern Diyala province, which borders the Islamic republic, the BBC reported last week. The conflict will test Iran’s ability to prop up its two closest Arab allies to preserve the political influence built in the region over the past decade. The collapse of Maliki’s government, without a pro-Iranian alternative ready to take over, would cut Iran’s leverage in its power struggle with regional Sunni powers such as Saudi Arabia and in its efforts to overhaul ties with the U.S. Related: “The fragility […]