Imperial Household Law
There were eight female imperial reigns (six female emperors including two who reigned twice) in Japan's early history between 593 and 770, and two more in the early modern period (Edo period). Although there were eight reigning empresses, with only one exception their successors were selected from amongst the males of the paternal Imperial bloodline. After many centuries, female reigns came to be officially prohibited only when the Imperial Household Law was issued in 1889 alongside the new Meiji Constitution.