You may not know this, but while your subjects are fickle and quick to anger, they are not too terribly bright. You don't have to spend a bunch of time and money training and equiping front line shock troops to keep the peace on all you worlds. You can simply slap a badge on an unarmed raw recruit and the ignorant masses will be suitably cowed by their mere presence.
(Translation: A cheap small troop unit with no weapon component will work just as well to increase happiness, and you can build many more per turn.
)
George