The consensus of all but the absolute most biased observers is that the decline in violence in Iraq has been due to a number of factors and not, solely, the result of the U.S. troop surge, The Sunni Awakening, the ceasefire called by Moqtada al Sadr and his Mahdi Army forces, new counterinsurgency tactics, and the influx of U.S. force into Iraq and, particularly, Baghdad all had a positive effect in reducing the level of overall violence in Iraq.
Long suspected, though perhaps never fully proven, has been the theory that there was yet another factor that contributed to the declining violence: ethnic cleansing by Shia militias in Baghdad. The February 2006 Sunni bombing of the Shia Samarra Mosque initiated massive retaliation by Shia militias against Sunnis, leading to a population shift from mixed neighborhoods in Baghdad. The resulting, homogeneous neighborhoods were without the intrasect tensions and, for all intents and purposes, now peaceful.
A new report, including evidence from satellite photography showing reduced infrared night imagery, shows the migration of Sunnis from mixed neighborhoods in Baghdad.
"By the launch of the surge, many of the targets of conflict had either been killed or fled the country, and they turned off the lights when they left," geography professor John Agnew of the University of California Los Angeles, who led the study, said in a statement.
Some 2 million Iraqis are displaced within Iraq, while 2 million more have sought refuge in neighboring Syria and Jordan. Previously religiously mixed neighborhoods of Baghdad became homogenized Sunni or Shi'ite Muslim enclaves.
The study, published in the journal Environment and Planning A, provides more evidence of ethnic conflict in Iraq, which peaked just before U.S. President George W. Bush ordered the deployment of about 30,000 extra U.S. troops.
Agnew's team used publicly available infrared night imagery from a weather satellite operated by the U.S. Air Force. "The overall night light signature of Baghdad since the U.S. invasion appears to have increased between 2003 and 2006 and then declined dramatically from 20 March 2006 through 16 December 2007," their report said. They said the night lights of Shi'ite-dominated Sadr City remained constant, as did lights in the Green Zone government and diplomatic compound in central Baghdad. Lights increased in the eastern New Baghdad district, another Shi'ite enclave. (Link)