No era-defining event, least of all a bloody and grinding decade of war, contains only one lesson for public policymakers and the society they represent. But the search for an overarching moral to the story is a valuable exercise, and we have asked some of the sharper minds on matters of war and peace to do just that. Here are their answers.

Eli Lake:

At the 20-year anniversary of the war in Iraq, there may be readers who expect an apology from those of us who supported the ending of Saddam Hussein’s regime in Baghdad. After all, by conservative estimates, the war cost more than $2 trillion. Since 2003, Iraq was beset by two fanatic insurgencies that killed and maimed hundreds of thousands of Iraqis, not to mention thousands of American soldiers. What has all that blood and treasure purchased?