How much of what we think of as reality is composed of popular delusion? Manipulating this shared delusion is an important part of any attempt to make it seem reasonable to kill or die for a country. Not only is it important to demonise the enemy but, even more fundamentally, it's important to make respectable everything being a soldier entails. In 1941, the year Japan attacked Pearl Harbour, a Kenji Mizoguchi film commissioned by the Japanese government called Genroku Chūshingura (元禄 忠臣蔵, "The Treasury of Loyal Retainers of the Genroku era") was released--called The 47 Ronin in the west because it is one of many cinematic accounts of the very famous incident from Japanese history. This rendition of the story does portray killing and, more prominently, dying for honour, and not for any intrinsically logical motives, as actions worthy of great esteem. The film was not successful with audiences, though, perhaps because this two part movie about samurai features almost no action and focuses entirely on the human compulsion to organise social perceptions. It's a fascinating film--commissioned to manipulate perceptions, it is instead a film about manipulating perceptions.
The only violence in the first of the two films occurs right at the beginning, when Lord Asano (Yoshizaburo Arashi) abruptly attacks Lord Kira (Mantoyo Mimasu) at a formal occasion of the shogun's court. This is also seemingly the one moment of simple human, animal behaviour though Asano's attack immediately follows a series of casually disparaging comments from Kira on Asano's character and abilities--Asano is apparently rebuking Kira for harming his reputation. When interrogated later, Asano never reveals the nature of his long-standing grudge with Kira or what prompted his extraordinary breach of etiquette.
From then on, the movie is about people massaging a certain truth into existence. The three men whom the shogun placed in charge of the investigation respond to hearing that Kira was praised for not drawing his sword by chuckling, remarking on what seemed to them to be cowardice on the part of Lord Kira. They are so impressed with Asano's composure and resolution, the lead investigator strongly insinuates to his superior the impropriety of condemning a samurai of Asano's family and holdings to death. But, the investigators are told, the decision has already been made by the shogun so it is inappropriate to submit an argument to the shogun now. All this is said while the shogun sits quietly in the next room behind a paper wall, likely able to hear every word, but the investigators know that any plea made directly to the shogun would not be valid because it was not arranged properly in rhetoric.
So Asano commits suicide on the shogun's order and his wife, in a solemn ceremony, cuts her hair short.
All this occurs in Edo--the city that would later be called Tokyo--where all samurai lords, daimyo, were compelled to live half the time, leaving their lands in control of subordinates, in this case Asano's castle is overseen by his chamberlain, Oishi (Chojuro Kawanami).
When the shogun orders the dissolution of the Asano family and resolves to take possession of the castle, the Asano samurai look to Oishi for guidance. Oishi commits himself to the cause of his departed lord, commands an oath of unquestioning fealty from the other samurai, now ronin (masterless samurai), and afterwards orders the abandonment of the castle in accordance with the shogun's orders. They must wait, Oishi says, until public and court opinion are in their favour.
He submits a petition to the shogun for the restoration of the Asano family and begins to frequent geisha houses in Edo to give the impression that he has fallen into a disgraceful lifestyle. It is only when the petition to restore the Asano family is denied that Oishi feels public sympathy is strong enough for the forty seven ronin to attack Kira's castle and decapitate him. It's not as though killing Kira is legal by popular vote--it's an illegal action regardless of public opinion. But Oishi knows that the revenge would be meaningless if it did not exist in a certain favourable manner in the public perception.
One might expect at least one big action set piece when the samurai descend on Kira's castle, fighting their way through guards until maybe a pitched battle with Kira himself, but the movie completely skips over the fight to the ronin begging Oishi to allow them to commit seppuku before their master's grave. But Oishi forbids it, knowing that the perceptual victory depends on the shogun ordering them to commit suicide rather than condemning them to the indignity decapitation.
So it's a story of elaborate revenge taken on a man who did not attempt to kill and did not order the death of their master and the ultimate goal is suicide. There are few or no practical motives. At one point the peasants who work the Asano land are mentioned but everyone agrees considerations of Asano family honour are more important than the basic feudal contract.