The history of Henry IV
As we look back from the twentieth century on Shakespeare's reconstruction of history, we are aware of at least two ways in which the plays are unreliable as history books: Shakespeare changed his sources to make the material more dramatic; and his sources themselves were biased in what they reported.
It is also a characteristic of history plays that they often benefit from some knowledge both of what happened before the action of the play begins, and of what happens after it finishes. Why did Henry depose Richard II? Are the rebels justified in their complaints? What dramatic ironies would audiences aware of later events perceive?