-Tim Cocks is a Reuters correspondent based in Baghdad.-
For the U.S. military, it's the million dollar question -- or rather the $687 billion question, according to a recent estimate of the Iraq war's total cost. Is Iraq now stable enough for them to take a permanent back seat?
The short answer is no one knows. The only way they were ever going to find out was to leave Iraq's own forces to it and hope the whole thing doesn't come tumbling down. They started doing that on Tuesday when they pulled out of Iraqi cities.
It's been an encouraging start. A big bomb in Kirkuk cast a shadow over Iraq's celebrations of its new-found sovereignty, but since then things have been relatively quiet. Militants might try to take advantage by stepping up attacks, but for the moment they seem content with celebrating a "victory" over the occupation -- and setting off the odd bomb, of course.
The United States' coalition partners have for the most part long since departed. British forces handed over southern Iraq to the Americans in April, but since 2007 their 4,000 odd troops left had been largely confined to Basra airport anyway.
And one thing the crystal ball gazers have learned about Iraq's hugely complicated, many-sided conflict is that the past is rarely a reliable guide to the future.