In Act 1, Scene 2 of Macbeth, there has been a battle raging. The King of Norway is in a conflict with the King Scotland. Part of the the major conflict is that the Thane of Cawdor is a traitor. He is a rebel and has allied with the King of Norway, going against King Duncan's men. Clearly, the Thane of Cawdor has deceived King Duncan:
The King of Norway himself, with terrible numbers of men, Assisted by that most disloyal traitor, The Baron of Cawdor, began a dismal conflict; Until the goddess of war’s bridegroom, disguised as truth, Confronted him with comparisons to himself, such as How they were both rebellious and both armed alike, Curbing his wild spirit. And, to conclude, The victory fell on us.
Thanks to Macbeth and Banquo, Duncan's men prevail and win the victory. Macbeth's and Banquo's swords become bloody weapons, sparing none of the enemy. Ultimately, the Thane of Cawdor is executed and the conflict ends. Macbeth is honored in his place and becomes the new Thane of Cawdor. At this point in the story, Macbeth proves himself a great soldier, worthy to lead as the Thane of Cawdor.