After reading the Fearon article for this week, I started to think about how rationalists would explain the Iraq and Lebanon wars. Here's how I see it:
Benefits Outweigh the Costs
This seems pretty obvious to me. The administration thought that Iraq wouldn't turn out the way that it has. Rumsfield said that we could draw down to 30,000 troops after a year, Wolfowitz said that oil revenue would pay for reconstruction, etc.
This applies to both Lebanon and Iraq because neither Israel or the US feel there is an international hegemonic power (i.e. United Nations) that exists to credibly threaten states with punishment when they step out of line. Saddam broke UN sanctions for over a decade, and Lebanon never disarmed Hezbollah after Resolution 1441.
This is Iraq from the standpoint that in the future Saddam could have nukes, and it was believed that he already possessed CB weapons. He had to be stopped before he gained too much power, and threatened the stability of the region.
Miscalculation Due to Lack of Info
This seems to be a stretch, but it could also be Iraq from the standpoint that we thought our European allies would join us in Iraq to prevent future threats. Hey, don't laugh. I said it was a stretch.
Miscalcuation About Relative Power
This is definitely postwar Iraq. The insurgents were seen as "dead-enders", and the insurgency was suppose to be in "its last throes" over a year ago. The biggest historical mistake of this war will be not planning for the strength of a postwar insurgency. The Israel-Lebanon war also fits this category. Israel was in no way prepared for how well armed and how well trained Hezbollah would be.