Royal Government

The Ōsei (王政) is the ruling system over the people of the Walls, consisting of a monarch and the assembly of nobles. Leading the nation from the capital of Mitras, the Fritz monarchy acts as the face of the Royal Government while the Reiss family acts as the true secret governing force of humanity.

History
It is said that the Royal Government held significance over humanity even before the Titans first appeared across the world, the royal bloodline having been unbroken for as many as 2,000 years.

During the reign of Uri Reiss, one of the noblemen of the Assembly informed Kenny Ackerman of the Reiss family's true royalty. After Kenny's attempt to assassinate Uri failed, this nobleman was removed from the Assembly and Kenny took his place.

The Uprising arc
After the operation where Eren Yeager was rescued from Reiner Braun and Bertolt Hoover, the Assembly summons Erwin Smith to chancellery in Mitras. During his meeting with the assembly, Erwin concludes that the nobility within the Royal Government cares only for their own positions and possessions, giving no regard to humanity as a whole. Conspiring with Dot Pixis, together they plan to overthrow the monarchy and appoint a new leader who will work towards the betterment of humanity and allow the Survey Corps to continue its attempts to reach Shiganshina District.

The opportunity to overthrow the Royal Government comes when Erwin Smith receives the news that the Reiss family is the true royal bloodline. After sending the Survey Corps to search for Rod Reiss, the true king of humanity, Erwin Smith is arrested by the Military Police Brigade, framed for orchestrating the murder of Dimo Reeves. When he is brought before King Fritz, the meeting is interrupted by Anka Rheinberger bringing false news that Wall Rose has fallen and Stohess District was under attack. The Assembly decides to close off the gates of Wall Sheena, refusing to accept any refugees. With this proof of the Royal Government's selfish nature, Commander-in-Chief Darius Zackly arrests the nobility and dethrones the Fritz monarchy.

Control over the nation of the walls is given over to the Military. After the death of Rod Reiss outside of Orvud District, Historia Reiss is publicly crowned as the new monarch of the walls. Members of the military take over the positions of the former Assembly.