What moral or other conflicts between different characters and different value systems bring about the tragic ending of Le Morte d'Arthur?
One conflict arises from the simple miscommunication of action. Both Mordred and Arthur, not trusting one another wholly, have instructed their men to fight to the death if any warrior on the opposing side should draw his sword. They distrust one another being that Mordred is Arthur's illegitimate son by his sister, Morgan Le Fay. Since Mordred is not claimed, he is unable to be the sole heir of Arthur's titles and lands. There is much bad blood and conflict there.
Of course, a warrior pledged to Arthur draws his sword to kill a snake that has bitten him during the feast. The miscommunication is that the sword is not drawn in malice, but simply for self-defense of the creature of nature. Unfortunately, the snake has caused the death of many men, including the famed Arthur, although some argue that since he was last seen floating on a barge with many beautiful women clad in black that he didn't die. Therein lies some of the mystery of the "Once and Future King" and the grave Bedivere later comes across which is tended to by a hermit.
Two "moral conflicts" help to bring down Camelot, and both deal with sexual immorality: adultery and incest.
One of the classic love stories of English literature is the triangle of Arthur, Guinevere, and Lancelot. Briefly, Lancelot betrays Arthur, they become enemies, and Arthur does not have his best knight when he needs him most.
Incest becomes an issue when Arthur's sister Morgan le Fey (or Morgause as some writers call her) deceives him into thinking he is sleeping with Guinevere. They have a son as a result. Mordred hates his father and fights to usurp his throne. Theirs is the final battle in the story.
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