It began right after the toppling of Saddam Hussein, when many landlords took advantage of the removal of his economic controls and raised rents substantially, forcing out thousands of families who took shelter in abandoned government buildings and military bases. As the chaos in Iraq grew and the ranks of the jobless swelled, even more Iraqis migrated to squalid squatter encampments. Still others constructed crude shantytowns on empty plots where conditions were even worse.

Now, after more than 10 months of brutal sectarian reprisals, many more Iraqis have fled their neighborhoods, only to wind up often in places that are just as wretched in other ways. While 1.8 million Iraqis are living outside the country, 1.6 million more have been displaced within Iraq since the war began. Since February, about 50,000 per month have moved within the country.