Fuedal Japan kept its structure by using multiple techniques to discipline its people.
Daimyo's were a big part in keeping control as they kept control in an area that the ruler distributed to them. He gave them this land because he trusted them, and in return they gave him control. They watched over his land and kept control of it. The Daimyos not only kept control of the land, but also kept the people within it safe and obedient. The use of Daimyos ended in the Meiji period.
Soldiers were also used to keep Japan stable, introduced in the Heian period, the samurai were strong and special warriors, that were the majority of the Japanese military. These warriors had a "code of honor" or a Bushido. These warriors helped keep structure by striking fear in the hearts of their enemies, while keeping their people safe.
Samurai were led by a Shogun. A Shogun controlled the military in Japan and acted as a general. They were protected by Samurai and were soon introduced to politics. They helped hold the empire of Japan together by deploying great military strategy into combat leading their army into victory
Minamoto no Yoritomo, the first shogun
Japan used many techniques to keep their empire together and these techniques helped inspire other things in our modern world.