Policy, collective punishment or free-floating retribution

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The resistance against the US isn't a ground-swell of dissent against it's occupiers as much as a second breath from guerilla soldiers looking to subvert a traditional war. Tikrit is where a good amount of them are based, and unless I got the map turned around in my head, it's also the portal to and from Syria. It's also near where Saddam had his terrorist country club.

Which doesn't really explain what they were targetting, if anything, but it's not as random as you're making it out to be.