In Macbeth, the English earl who leads the invading army is Siward, Earl of Northumberland. He commands the English forces that enter Scotland to oppose Macbeth and support Malcolm, Duncan’s son and rightful heir in the play’s political order.
Siward’s invasion appears near the climax of Shakespeare’s tragedy. Malcolm joins the English army and orders each soldier to cut a branch from Birnam Wood and carry it toward Dunsinane. This disguises the army’s size and fulfills the witches’ prophecy that Macbeth will be safe until Birnam Wood comes to Dunsinane. Siward’s forces then help defeat Macbeth’s defenders.
The historical Siward was an important eleventh-century Anglo-Danish nobleman and earl of Northumbria. Historical accounts connect him with an English campaign against Macbeth in 1054, although Shakespeare compresses and reshapes the events for dramatic effect. In the play, Siward’s son Young Siward is also killed in single combat by Macbeth, who claims victory over him before facing Macduff.
A common mix-up is Malcolm: he is the claimant whose cause the invasion advances, not the English commander. Macduff leads the personal challenge against Macbeth, while Banquo belongs to the earlier part of the story.