The Empire of Rokugan is still small and surrounded by threats. Barbarians in the north and west, pirates from the east, the shadowlands to the south, yokai everywhere, and eventually Iuchiban and his bloodspeakers.
The descendants of Bayushi, Shiba, and Doji maintain the alliance that gave Hantei the throne, mostly to keep the Akodo out of power. Old retired Emperors have long "advised" their young replacements to a large enough extent to be de facto emperors, and with the tradition of Emperor/Doji marriage, the prestige of the Isawa school, and the tactical importance of Bayushi, it wasn't particularly hard to make the Emperor their puppet.
It seems fitting to name this era