Israel declared war because...

With the Israeli declaration of war on Hamas, Israel conceded Hamas being a political entity with a fighting force in control of Gaza. It did so to make Hamas responsible for the evacuation of civilian's from the battle area as Israel defined being the northern part of the Gaza strip. Hamas telling the population in northern Gaza to stay in place constitutes a war crime, or at least an appeared abdication of it's responsibility as the local controlling party (to an armed conflict) to ensure the safety of civilian's. Going beyond individual images of suffering and looking at the logic of this within the tradition's of each party: Offering up civilian's for "the cause" seems just an extension of killing the other parties civilian's if you've already decided the death of civilian's isn't haram.