I am specifically talking about going to war that is a mitzvah such as the wars fought while conquering Eretz Yisroel in the beginning of the Neviim and the mitzvah we have and will fulfill of destroying the entire nation of Amalek. I have not seen anything written on what the Torah perspective is for the soldier going and killing people when done as a mitzvah. (Are you supposed to be besimcha? Are you supposed to have a part of you not like what you are doing?) As always sources for ideas will be most appreciated.