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I disagree that invasions have better reasons or at least more comprehensive reasons.
I think the key is to understand there is no foreign policy in any `big picture' . Bush Senior had a problem with big pictures. Bush Junior had no big picture, but he subcontracted the big ideas to the neocons, who thought they had a big picture. Clinton did the same thing with the old school cold war liberals. It's a Reagan thing. Obama has no big picture but he has a committee of big picture types and he is trying to sort out a `consensus' big picture. Unfortunately, there is no big picture collage that seems to make sense, hence the foot dragging on every important issue. So whatever the decision, it won't make sense, because there is no sense to be made.
CG