Page 5 of the basic rules, key concepts .......
Provinces and Strongholds
A player’s province cards represent a variety of circumstances and occurrences in the lands under the control of the Great Clans of Rokugan. During the game, players declare attacks against one another’s provinces, and successful attacks can result in a province breaking. If three of a player’s four non-stronghold provinces are broken, attacks may be declared against that player’s stronghold province. As soon as a player’s stronghold province is broken, that player loses the game.
PRETTY SIMPLE you must have missed it


