LOL, so all of a sudden they decided that the time is ripe to start taking out the other party (sunni/shia).before the war there was relative calm between the 2 schools of thought even mixed neighborhoods(shia/sunni neighbourhood) even while did have their differences - no tension
These battles between the two Muslim groups existed and continue to exist without the link to a specific "war".
I've seen it in Pakistan where one group paraded the streets flagellating themselves (great practice - should use sharper implements), while the other group sniped them from the buildings.