Is it okay for an Orthodox Christian to join the military?

Not really much to say. I mean, every Orthodox country has a military. The military is supposed to be there for the defense of the homeland. We have many Orthodox saints who were military people who fought in the Roman Empire. All you have to do is Google Orthodox warrior saints. There's whole books that are written on them. So we don't have any problem with defense of the homeland or military service. What we would not want to participate in, ideally, is wars in other countries and lands that are for profit or the military industrial complex, but don't have to do with the safety of our homeland. Ideally we would not be participating in those.