Are soldiers sinning when they kill enemy in a war?

Soldiers are like slaves to their commanders and have to do whatever they are told to do. If not, in war like situation, they can be punished by their commanders. So will the soldiers be accountable for the killing they do ? The question came to mind because of the recent war in Palestine. The jews who are fighting Palestinians are doing so because they have to do compulsory military service, so even if they dislike killing people, they are compelled to do so. Note: I have asked same question in Judaism section also. Actually Muslims and Jews are brothers who are descended of our patriarch Abraham (Peace be upon him), It is sad to see them fighting each other, I feel like they are forced to fight each other by some who have vested interest in this conflict.