Because their operation failed badly--and the Iranians had to cut their losses.
That scenario--which we've advanced in previous posts--was echoed in a Thursday op-ed piece from Amir Taheri, published in the New York Post. In his column, Mr. Taheri raises the same question we did when the Battle of Basra lurched to a sudden halt, with assistance from Tehran. If the operation was going so well, why not press ahead an inflict a political and military defeat on the Iraqi government?
Instead, the commander of the Iranian Qods Force--the same organizations that trained the equipped militants involved in the uprising--brokered a quick cease-fire with Iraqi politicians. His motivation was clear; without a cessation of hostilities, Iranian-backed insurgents faced the prospect of even greater losses, and humiliation at the hands of the Baghdad government.
And, the Iranian failure wasn't limited to Basra. Planning Shiite revolts in other regions failed to materialize. Senior clerics sided with the government, and the Iraqi Army performed well in its first major, semi-autonomous operations. Faced with a battle its proxies couldn't win, Tehran had no choice but to pull the plug.
Iran's defeat in Basra was a victory for the al-Maliki government and its security forces--though many western media outlets tried to depict it as an Iraqi version of the Tet Offensive. But any celebrations in Iraq (or elsewhere) should be tempered by this obvious reminder, offered at the end of Taheri's column: "This was just the first round. The struggle for Iraq isn't over."
Indeed, we've participated in more than a few war games that feature Iran's attempted annexation of southern Iraq, as a prelude to wider operations in the Persian Gulf. Tehran is patient, and learns from its mistakes. There will certainly be a second Battle of Basra, and perhaps sooner, rather than later.