Rulers: Core Rulebook

Rulers is a tabletop roleplaying game of conquest and politics, where players will craft their own civilization, and forge their own dynasty. The game is played with 4-6 Players and 1 Narrative Overlord, whose job it is to “referee” the game. To take actions in the game, Players will send Reports to the Narrative Overlord by email, letter, private courier or carrier pigeon (as you prefer). This book - the Rulers: Core Rulebook - details the Rulers System as well as the instructions on how to play the Rulers roleplaying game.

From the rulebook's introduction.