How did Kurosawa turn Macbeth into a samurai film, and why do Shakespeare's plays travel so well?

Kurosawa kept the plot and threw away almost everything else. In Throne of Blood (1957) a warrior assassinates his sovereign at the urging of his ambitious wife, as in Macbeth, but the setting moves from medieval Scotland to feudal Japan and the style is drawn from Noh drama. Shakespeare's poetry is gone, and critics still argue over what that leaves.

Shakespeare had long been read in Japan, since the Meiji Restoration in 1868, although his plays were banned during World War II for not being Japanese. Kurosawa had admired Macbeth for a long time, and he put his film off for several years after learning that Orson Welles had made a Macbeth in 1948.

So the witches become an evil spirit in the Spider's Web Forest, and where Macbeth is told he is safe until Great Birnam Wood comes to Dunsinane Hill, Washizu is told he cannot be defeated until the trees of the forest rise against the castle. In the death scene his own archers turn on him, and the arrows were real, shot by skilled archers. Critics argued about what to call it: Peter Brook considered it a masterpiece but denied it was a Shakespeare film because of the language, while Harold Bloom judged it the most successful film version of Macbeth.