Let us deal with the haftara, which discusses David’s instructions to his son and successor, Shlomo. David instructed Shlomo to execute Yoav, his top general, for having killed rivals, Avner and Amasa, who had lead troops opposed to David before reconciling with David. David explained that he had "placed the blood of war in peace" (Melachim I, 2:5). What does that phrase mean?
Rashi and the Targum explain that Yoav used trickery to kill the unsuspecting who thought they were at peace with him. This explanation is difficult as it does not seem to be grounds for punishing Yoav. If Avner had deserved death, what difference did it make that he used trickery to accomplish the just outcome? If he did not deserve to be killed, would it have helped to have killed in a straightforward manner? The phraseology of war and peace are also problematic, as these are terms that refer to the relationship between national or factional groupings, whereas Yoav acted against personal rivals?
The gemara (Sanhedrin 49a) discusses at length the legal argument between Yoav and Avner before the latter’s execution. Apparently Yoav killed him not with the claim that Avner had rebelled against the kingdom but for killing Yoav’s brother Asael during the civil war. Asael had chased Avner during battle. Avner warned him to stop pursuing him and, when he refused, killed him. The crux of the debate was whether Avner, who was clearly a superior warrior to the fleet-footed Asael, had needed to kill Asael in order to save his own life. The gemara concludes that Avner could have sufficed with injuring him, and thus Yoav had some justification to kill his brother’s murderer. Before understanding Yoav’s culpability, we need to introduce a new concept.
It is not always clear when a situation of war-like tension and sporadic fighting qualifies as a war. Note, for example, that the fighting in the summer of ’06 in Lebanon was not initially considered a war. The bloodshed in the many terrorist attacks over the last two decades and our responses to them have also not been seen to qualify. The differing rules of engagement between peacetime and wartime make these distinctions potentially critical. Does one warn an attacker to put down his weapon or does one just charge the attacker and kill him?
David and Yoav argued a question of this nature in regard to the tensions and battles between the supporters of Shaul’s family’s claim to the throne and David’s. David consistently considered it peace time, in which case, one who could have saved his life without killing another had to do so. Yoav and his brothers reasoned that there was a civil war that warranted killing. Therefore, by Yoav claiming that his brother’s death was murder and not death during battle, he was contradicting himself in mixing the concepts of peace and war.