Thousand Years of Peace

According to Shinsei, once every thousand years the champions of Yomi must face the champion of Jigoku on the Day of Thunder to determine whether the next thousand years will be a Thousand Years of Peace or a Thousand Years of Darkness. The last ten centuries have been a Thousand Years of Peace, but only in a certain sense of the word.

Peace
The term peace may seem a vast understatement considering the countless wars between clans that have been fought in the last thousand years. But, these civil wars, and even the rise and fall of Iuchiban, pale in comparison to the battle against a Kami, Fu Leng. Historians use the phrase peace to show how close the fledging empire came to being unmade by the Dark Lord; that every war since the first Day of Thunder is nothing when compared to the power of Fu Leng.

Cold War
The Shadowlands is a constant threat outside Rokugan's borders. However, most creatures are content to stay within and there have only been a few major invasions of the Empire, such as the Battle of the Cresting Wave. On the other hand, any large scale invasion of the Shadowlands by the Clans has been disastrous. It is impractical to station an army near the Black Finger River and too costly for the empire to manage, an idea greatly supported by Crane and Otomo courtiers trying to stop the Crab Clan from gaining power. Without Fu Leng's physical presence, the horde is undirected and unfocused. Until Fu Leng is restored, the Shadowlands is content to wait as it gains more allies and seeps slowly into the Empire.