The first gulf war, Operation Desert Storm, was deliberately limited in scope -- liberate Kuwait from Iraqi control. Its predecessor, Desert Shield, as similarly scoped, to prevent an Iraqi invasion of Saudi Arabia. Both were successful by the metrics set out for it. Bush Sr. got a lot of flak from the burgeoning neocon movement for not driving through to Baghdad, a decision which in retrospect was incredibly correct.
Afghanistan and the second Iraq war, and the various "police actions" undertaken since then, have objectives that are unclear or are metric-based and do not easily translate to a simple objective that can be reasoned to be a stable endpoint. In this, it seems that the military is following suit with general industry trends towards vaguely defined metrics and objectives that allow for technical "success". This approach was pioneered, really, during the Kennedy administration with our approach to Vietnam and the "domino theory".