Its not so much what Bush senior wasnt able to do so much as what he was advised NOT to do by the chairman of the joint chiefs.

Full scale invasion and occupation was something which Cheney was allways pushing for and was completely in disagrement of his boss's desicion. (he was in Bush senior's administration under donald rumsfield at the time).

Many people (most of the public not aware of the stategic situation) didnt understand Bush seniors decison at the time and still dont in many instances.

Powell and many advisors pointed out that if an invasion was carried out it had to start with an overthrow from within to secure popular support (hence why the kurds and others were initially being urged to rebel) and that it would ultimately destabilize the region for decades making a power vaccum that Iran would try to fill, unless the US was prepared for a another long term occupation like those in Germany and Japan.

GW along with Chenny (holding more power and influence than any VP ever had before) apparantly decided to go with a long term stratagy. I am certian Chenney had a lot to do with the decison. He has allways had an axe to grind in this area. He went round and round with the CIA on the intellegence and insited several times despite thier disclosure of lacking proper information on pressing the issue. No surprise there for any student of history.

Regan's stratagy for the cold war is a little more off topic and should probably have it's own thread.