Re: What lead us to this situation in Pakistan.
a few points about your post
a) Regardless of your explanation of motivations of these groups, the thesis of your argument that terrorism in Pakistan did not exist eight years ago is pretty much defeated. It did exist and thousands (according to amnesty, close to 3000) of people died. I can actually tell you of a suicide bombing in Karachi way before any of all this started.
b) The fighting was extremely lopsided. If you reference amnesty or hrw for that period you'll see an overwhelmingly larger number of bombings and deaths of shias compared to sunnies
c) Many of the groups associated with terrorism now are actually familiar figures to shias, having been associated with terrorism back then too. You obliquely mention Iran as being a winner in this situation, presumably you are aware of that too, that terrorists who previously bombed imambargahs are not being patronized anymore (if they previously were)