From the introduction:
The Koga family is a ronin family who can track back her history to the dawn of the Empire. They have never been recognized as a family by the Emperor, but they still cling to the title, that came from the traditions of the tribes that lived in Rokugan before the fall of the Kami.
The Koga have a long and shadowed history. They was in the past a tribe of humans that lived peacefully (meaning they fought from time to time their neighbors, and some others times trading with them, depending of the leader and the situation) near Mizu-umi no Sakura Yuki (Lake of blossom snow, EEE on the map) south of the Dark forest (the little forest east of the end of Shinomen).