The sanctions regime, which began in 1990, destroyed Iraq’s economy (reducing GDP by as much as three quarters) and impoverished millions of Iraqis. Particular attention was given at the time to its effect on children. The contemporary critics of the sanctions pointed out that before the sanctions began, the child mortality rate was about 50 per 1000; during the sanctions, on one accounting the rate soared to about 128 per 1000 (click on "basic indicators" here). More conservative estimates were in the range of a doubling of child mortality. Using the more conservative estimate, at one million births per year, this works out to an annual difference of 50,000 children surviving to the age of 5 (for various qualifications, see here). Today, the child mortality rate is below the pre-sanctions figure, and so every year in excess of 50,000 more Iraqi children survive than during the sanctions. The data are hotly contested but the trends are unmistakable and will continue to strengthen if security improves. Meanwhile, violent deaths of civilians, while still far too high, are declining; a very cautious estimate of 500-800 per month, based on the most recent reports on the Iraq Body Count website, is much lower than the avoided deaths of children compared to the sanctions regime. A conservative estimate is that more than 40,000 Iraqis survive per year today than during the sanctions regime, and probably most of them children. The tight correlation between GDP and child mortality across countries bolsters this conclusion.
Let’s suppose that the sanctions regime had continued for 10 years, from 2003 to 2013, and further that security flattens out—it doesn’t get worse, but it doesn’t get better. Under these assumptions, 400,000 Iraqi children would have died if the war had not occurred and the sanctions regime continued. Now, almost 100,000 Iraqis died during the war, and so one of the war’s benefits is that it saves the lives of 300,000 Iraqis (over 10 years).
I have always been suspicious of child mortality estimates during the sanctions period, and of old data in general. I just link to this piece to highlight the difficulties in honestly estimating "excess deaths." All of this also ignores the question of what Saddam's policies would have been had he stayed in power. If he would have been as "peaceful" in the future as he was in 2002, then excess deaths is one number. But, if he had become less peaceful (more in line with the previous decades of neighbor-invasion (Iran, Kuwait) and internal-slaughtering (Shia, Kurds), then excess deaths are much lower, even negative, as a result of the invasion.
But, as always, my main focus is on the Lancet surveys. They make an explicit comparison to mortality in 2002 to March 2003, so these discussions are largely irrelevant. (Hat tip Andrew Sullivan.)