Jewish Military Ethics

(7) Then Jacob was greatly afraid and was distressed. And he divided the people that was with him, and the flocks, and the herds, and the camels, into two camps.

Jacob was afraid, lest he be killed. And he was distressed, lest he kill others.

One can explain that Yaakov was afraid that he kill Esav and Yitzchak would be exceedingly upset, of the loved Esav and Esav remained in good standing in the eyes of Yitzchak, such that Yitzchak would then curse Yaakov (Tanhuma). Alternatively, one can say that Yaakov was certainly not afraid to kill Esav since we have established (Sanhedrin 72) that one who arises to kill you - go first and kill him. Rather, Yaakov was afraid less he kill the men in Esav's army. Perhaps they did not come to kill Yaakov but only Yaakov's retinue and only Esav himself came to kill Yaakov. And even if the men in Esav's army were pursuers trying to kill the men in Yaakov's retinue, and any person is permitted to save one who is being pursued even at the cost of the life of the pursuer (Sanhedrin 73), nonetheless if it is possible to stop him with a non-lethal injury and he kills the pursuer anyway, the one who kills can be executed by the court for murder. And Yaakov was worried lest he kill them in the midst of the fog of war someone who could have been stopped with non-lethal force.