Before the 2003 invasion, estimates for Iraqi internally displaced people (IDP’s) ranged from 800,000 to 2 million. Conservatively, 1,250,000 Iraqis are thought to have fled the country during the 12 years of UN sanctions. In the years following 2003, Iraq’s refugee problem has grown into what many observers regard as an unprecedented crisis.  One in twelve Iraqi families have fled their homes and not returned . A population shift on this scale has not occurred in the Middle East since the establishment of the state of Israel and the displacement of Palestinians in 1948.
What many experts call a “silent crisis” has impacted not only the lives of the 2.8 million Iraqis currently uprooted from their homes, but also the communities and social fabric that those fleeing have left behind. Engineers, artists, lawyers, academics, doctors, and other professionals were among the first to escape the war. This migration drained Iraq of its middle class. It dismantled many of Iraq's cultural and educational institutions sustained by teachers and artists. And it stripped a society of the many services that such professionals provide.
According to figures published by the Iraqi Medical Association, approximately half of Iraq's 34,000 registered doctors fled Iraq in the years immediately following the 2003 invasion. Targeted by armed militias and gangs, thousands of doctors have been held for ransom, killed or wounded. Some doctors have returned and new doctors have been trained, but the Iraqi government's current figure of 25,000 practicing physicians remains well below the pre-invasion level, putting Iraq significantly behind neighboring countries in terms of patient/doctor ratio. 
Meanwhile, crucial health indicators in Iraq have drastically worsened. The infant mortality rate increased 150 percent from 1990 to 2005, the worst retrogression in that basic indicator of well-being in the world. The World Health Organization estimated that 70 percent of Iraqis lack access to clean water and 80 percent lack sanitation, conditions leading to epidemics of cholera. In short, the war has brought increased rates of illness and disease to Iraq, while displacing the very medical professionals who could have treated Iraq's sick.
The displacement of millions of Iraqis has also reconfigured the ethnic and religious composition of neighborhoods. The bombing of the Al-Askari mosque in Samarra in 2006 incited sectarian violence by militant groups and led to a second wave of forced migration in which many Iraqis fled. Their departures left neighborhoods and governorates in once plural cities like Baghdad and Diyala ethnically homogeneous for the first time. Studies have shown that the drop in sectarian violence after 2007 was not a result of the US and Iraqi military surge, but a consequence of ethno-religious homogenization. As each group and sub-group claimed its own territory, there was no one left to kill.
There is little hope that the diverse population that Iraq has lost will be regained any time soon. Few refugees plan to return. As one Iraqi engineer who now works in a restaurant in Damascus stated, “There is no Iraq to return to, my friend. Iraq only exists in our dreams and memories. (Text updated as of March 2013)
IMAGE on Iraq anniversary page: By José Goulão (flickr)
 Chatelard, Geraldine. Constructing and deconstructing the ‘the Iraq refugee crisis.’ Paper presented at the conference of the International Association of Contemporary Iraqi Studies, SOAS, London, July 2008.
 Displacement data taken from the UNHCR Country Operations Profile, Iraq (January 2012). Population data taken from Population Reference Bureau mid-2012 Iraq Profile.
 “Iraq: Putting People First,” 2013, The Lancet, Vol.381 (9870), p 875.
 Save the Children, “No Child Born to Die—Iraq,” (October 18, 2012), http://www.europarl.europa.eu/meetdocs/2009_2014/documents/d-iq/dv/d-iq20121018_07_/d-iq20121018_07_en.pdf.