From the back of the book:
The Essential Handbook for REIGN
REIGN: A Game of Lords and Leaders expands the frontiers of fantasy roleplaying games by elevating the action to an international stage. Monarchs, mercenaries and merchant princes gamble armies and fortunes to win nations. REIGN's simple but complete rules model the triumphs and disasters of societies as small as a village or as large as a realm-spanning religion. With REIGN, your characters can defend threatened nations, bring prosperity to desperate provinces, make laws and perpetuate justice… or, if you prefer, loot, conquer and pillage on a vast and awesome scale.
The REIGN Enchiridion contains all the essential rules from REIGN, plus the most useful material from REIGN's supplements.
One Roll Does It All
Powered by a fantasy-optimized version of the One-Roll Engine (or ORE) popularized by Godlike, Wild Talents, and Monsters and Other Childish Things, REIGN can take your characters from beggars to emperors. The ORE resolves events in delicate detail without cumbersome layers of contingent rolls.
The Personal and the Political
The group-resolution rules from REIGN are self-contained and modular. It's a simple matter to stack them on top of any other RPG system. Want a concrete way to model what happens to the city when your superheroes destroy the Cult of Moloch Triumphant? Use REIGN to stat up the city and the cult. Ever wonder who'd win if two rival government conspiracies went head to head? REIGN lets you measure their weaknesses and strengths, then test them against one another. Fantasy kingdoms, cosmic empires and secretive cabals can all be easily managed and modeled with REIGN.