Mentsch1: Do you really believe the rishonnim would argue against tanaaim (this is an explicit Mishna is Sotah)? Also, I never said mixed. I said they can be in the army.
mdd1: Actually, I believe that is incorrect. According to the Rambam (perek 5), he needs to ask permission from the Sanhedrin if he takes the “people” to a discretionary war. But I do not believe this applies to his own army. He can wage war using his army without permission of the Sanhedrin. In addition, even the rambam agrees that fighting for the survival of Israel and Jews would fall under a Milchemes Mitzvah which does not require the Sanhedrin’s approval .
Regardless of the halacha, in hindsight, if our kings actually listened to the Sanhedrin we would not be in today’s galus and our history wouldn’t have been so bloody.