It does get a bit confusing! The Norwegians are attacking King Duncan and Scotland. Allied to the Norwegians are two Scottish traitors, the 'merciless MAcdonwald' and that disloyal traitor the Thane of Cawdor.
Macbeth is responsible for defeating Macdonwald and 'fixed his head on our battlements.'
The captains loyal to Kind Duncan are Banquo and Macbeth and they are described as loyal, valient and bold. After the defeat of MacDonwald the 'Norweyan lord surveying vantage with furbish'd arms and new supplies of men began a fresh assault,' aided by Cawdor. This is also defeated by the Scottish and Macbeth is to gain lands and the title of Cawdor is given as a reward to MAcbeth, this is ironic that Macbeth is rewarded for loyalty as he very disloyal himself in the later scenes.
In Macbeth, one of the first signs that "fair is foul and foul is fair" (I.i.10) is the talk of treachery in Act I, scene ii when MacDonwald, a Scottish soldier, is exposed as a villain. It is ironic that it is Macbeth who apparently stands firm against MacDonwald and fights against him until he is victorious. As the scene says, Macbeth "unseamed him" (22). "Brave Macbeth" (I.ii.16) and Banquo are returning from battle against the king of Norway and, even though the king of Norway tries to take advantage of their apparent preoccupation with MacDonwald, they maintain their vigilance and military prowess upon a fresh attempt from the "Norweyan lord" (31) and fight against him.
Furthermore, the Thane of Cawdor is also exposed to Duncan and his men as a "disloyal traitor" (53) who takes up arms with the King of Norway and begins "a dismal conflict" (54) which the Scots win.
The unsettling circumstances continue and are confirmed by Macbeth when he talks to Banquo of the "foul and fair" day (I.iii.38), and witnesses the strange appearance of the witches who, as Banquo says, "should be women" (45) but clearly are not what they appear. They prophesy that Macbeth is to be Thane of Cawdor and, more surprisingly, king. Macbeth is startled by their appearance and their claims and is unable, at first, to process the information.
In Act I, scene 2 of Macbeth, both Macdonwald and the thane of Cawdor are traitors against Scotland, while Macbeth is a hero fighting for Scotland. The reader learns that "The merciless Macdonwald-- Worthy to be a rebel" was fighting against Macbeth, who defeated him. Therefore, Macdonwald was a traitor to Scotland. As the sergeant says, "but all's too weak:/ For brave Macbeth." Macbeth, the Scottish hero, treats his rebellious enemy, who has deserted the Scottish side, with no pity. Instead, "he unseam'd him from the nave to the chaps,/ And fix'd his head upon our battlements." In other words, Macbeth sliced off the head of the the rebel Macdonwald and placed it on the top of the wall. For his bravery in battle, Duncan, the king, rewards Macbeth with the title thane of Cawdor at the end of this scene.
Ross appears to tell the king that the thane of Cawdor has, like Macdonwald, been a traitor in the battle between Scotland and Norway: "Norway himself,/ With terrible numbers,/ Assisted by that most disloyal traitor/The thane of Cawdor, began a dismal conflict." For this reason, Duncan tells Ross to have the thane of Cawdor killed. Duncan says, "No more that thane of Cawdor shall deceive/ Our bosom interest: go pronounce his present death,/ And with his former title greet Macbeth." In other words, the thane of Cawdor will be killed for being a traitor, and his title will pass to Macbeth. This is the honor that Macbeth receives at the beginning of the play, and it makes him hungry for more power.