Japan was a feudal society. There were several social classes (outlined below), and people could rarely, if ever, leave that class. Japan was similar to Europe in that way. Japan was basically an isolationist society, not until British Commodore Matther C. Perry sailed into Edo harbor in the 19th century did Japan open its door to free trade. Honor was prevalent in the warrior class, samurai regarded dishonor and going against one's lord a fate worse than death. Some held elitist views, and look down on commoners and ashigaru, and considered ninja and ronin as cowardly.
The Emperor is the ruler of Japan. Often the title is a spiritual role, and the Shogun holds the military power. He resides at Kyoto, but during the Tokugawa period in Edo (Tokyo). The Emperor often becomes a monk, because he is granted more freedom. The Fujiwara family married into the royal family, and gained sway of Japan quickly.
Shogun:
The Shogun is the military leader. The Shogun was headquartered in the capital (name of period), and is basically subservient to the Emperor. No Shogun would fight the emperor, but often times the Shoguns influenced the Emperor's decisions.
Sessho:
Sessho are the Regents. They work directly for the Shogun, and are his top generals.
Kuge:
The Kuge are aristocrats. They reside in great palaces, and pursue a life of the arts. Many wrote novels, and were the families and rich servants of Lords.
Buke:
The Warrior Class
Daimyo:
The Daimyo is a military leader. They are governors of an area, and fight to control land. They will often become more passive when under a Shogun's threat, but during the civil war period, they all fought to control Japan. There are three forms of daimyo, the Shimpan, lords related to the royal family, Fudai, hereditary lords who controlled fiefs, and Tozama, who were lords hostile to the government.
Samurai:
The main warrior class. They believed in a strict honor system and the way of the Bushido. The title 'Samurai' is a broad term, but generally in encompasses all warriors, from daimyo to the poor bushi. All samurais owned land and rice fields. They were completely indebted to their lord, and would commit seppuku if captured.
Ashigaru:
The ashigaru were footsoldiers. They were generally poor, didn't own land and didn't follow bushido as closely as the samurai. They used many weapons rather than the sword, and fought on foot. They are also known as bushi.
Ninja:
Ninjas were masters of espionage and assassination. Many samurai regarded them as 'dishonorable', a fate worse than death to samurai. They were usually employed as mercenaries, and were dispatched to spy, survey, sabotage, assassinate, etc. They struck at night, and tried to leave no traces. They employed poisons and deception.
Ronin:
Ronin were masterless samurai. Although traditionally considered a dishonor to be a ronin, it was not necessarily so. The traditional saying 'seven times down, eight times up' describing how a lord would periodically dispatch bushi on a year-long wandering mission.
Bonge:
The Bonge were peasants and merchants, the lower class.
Ryoke:
Ryoke were landowners and independent farmers. They were richer than other Bonge and employed bushi for protection.
Gesakunin:
They were renters and tenant tarmers. They rented land owned by a daimyo or Ryoke.
Zomin, Nuhi, Genin:
The merchant class. Unlike medieval Europe, the merchants in Japan were considered to be below the peasants. This is because they made money off of others, and were considered 'dishonorable' because of that.
