Advance
Postal Service
With communications being what they are, it is difficult to ensure that our diplomatic dispatches arrive in a timely fashion. Creating a network of post offices and courier rest stops will make it easier for our voice to be heard in distant lands.
Advance tree
The game files don’t say where this goes: it has no requires, so the game places it in the 
Revolutions tree itself.
Modifiers
Definitionin_game/common/advances/4_choices_dip.txt:438
440icon = road_building
441for = dip