A lot of countries(Nazi Germany, Saddam's Iraq, the Soviet Union(arguably), various other Arab countries(including Saudi Arabia), the Islamic republic of Iran)...
Have dual militaries-meaning they basically have two militaries that counterbalance each other-Hussein had the regular military and republican guard, hitler had the Wehrmacht and SS, The Islamic Republic of Iran had the conventional Artesh and the IRCG, etc...
One force is often more external defense or attack and the other closer to the regime ideologically or otherwise.
How can we have a triune military structure where three militaries compete and counterbalance one another within a state?