Can a military career be ethical?

There are military generals as lay people and stream enterers in the suttas. And there is no clear prohibition to a military career. There are some suttas that criticize the karma of soldiers on the battlefield. My question is, since being a military general is acceptable livelihood, what should he do? Could he planning for war, making war, or just sit there and do nothing since both of those actions could lead to indirect killing? If he does nothing, that can lead to catastrophic results and even more people maybe get killed. Is that right livelihood if other people rely on him and he has the responsibility to use military force to protect people?