A state agent is a non-military unit that a country gets, that it may send places to attempt a variety of actions. The term "state agent" is not commonly used by players. Rather it is a phrase made up for the EU2 wiki as a place to discuss common attributes of the types of state agents.
There are four kinds of state agents:
- diplomats, sent to countries to attempt diplomatic actions
- colonists, sent to provinces to attempt colonization (including trading posts)
- missionaries, sent to settlements to attempt religious conversion
- merchants, sent to centers of trade to to attempt to gain trade
All kinds of state agents are finite. They are used up in attempts to do what they do (see above), almost always one per attempt. The amount of them of each type that a country has is a floating point number, ranging from 0.0 to 6.0. Onscreen, this number is truncated (rounded down); you can see it in a save game if you look.
New agents are added at each month end; because the amount is usually fractional, you will not see the increase in-game until some months pass. It is possible to lose state agents at month's end, but only colonists in vanilla EU2. (Diplomats and merchants cannot have negative gains, and missionaries are protected from loss by special rule.)