In accord with the setting of the play, the customs and titles held by the characters in Macbeth reflect feudal traditions and clearly reveal a feudal government. The main tenet of feudalism is the exchange of vows, described by Galbert of Bruges: "The count asked if he was willing to become completely his man, and the other replied: 'I am willing;' [...] Afterward...[the count] gave investiture to...who by this agreement had given his...oath" (Sources, Section 7-7, pg. 216). The count gives his vassal a reward in return for loyalty. In Macbeth, Duncan condemns the traitorous Thane of Cawdor to death and simultaneously gives Macbeth a second fief for his victory in battle (Macbeth, Act 1, Scene 3, ll. 74-76). These actions are a disguised and cunning attempt to ensure or strengthen the unwavering loyalty of Duncan's vassals. Macbeth replies by stating that "your Highness' part is to receive our duties...safe toward your love and honor" (Macbeth, Act 1, Scene 4, ll. 26-27). This dialogue itself illustrates a subtle 'exchange of vows' described by Galbert. As it is the equivalent of a contemporary written contract, breaking the oath of loyalty given during the ceremony of investiture is a severely punished act of treachery. Hence Macbeth ponders the immorality of his assassination plot: "He's here in double trust: First, as I am his kinsman and his subject, strong both against the deed" (Macbeth, Act 1, Scene 7, ll. 12-14). Lastly, the titles and personalities of the characters themselves are feudal (for example the various "Thanes") - clearly portraying a stable feudal world.
However, Shakespeare, as a playwright in monarchial England, understandably also exposes and illustrates the basic flaws of feudalism. The feudal pyramid consisted of "many knights...with a small fief", above them their royal vassals "who held larger fiefs", and "over all...the king" (W.H, Section 9-4, pp. 215). Maintaining order among the powerful nobles was a difficult task for any ruler; only a strong king would be able to exercise authority and keep any revolts or rebellious acts to a minimum or at least in complete check. On the surface, Duncan seems to fit this description. According to Macbeth, he is "so clear in his great office...that his virtues will plead like angels" (Macbeth, Act 1, Scene 7, ll. 18-19). However, both Macdonwald and the Thane of Cawdor start a revolt against the King, who depends on his other, loyal, thanes to crush the uprising and capture the traitors; apparently, he personally does not participate. Feudal lords and vassals were expected to participate in war (Bertran de Born, Sources, Section 7-7, pg. 217), and Duncan's inability or unwillingness to direct his armies is a weakness. (If the Thanes decide to remove him from his throne, there is little the king can do against it.) This shows the primary 'loophole' in the feudal system: if the king of a host of vassals is weak, then he becomes a figurehead rather than an actual leader, and the entire area is further decentralized and isolated as vassals become more independent. Although this flaw is usually inevitable, Macbeth presents an even more critical view of the matter - the assassination of Duncan by Macbeth, who replaces him. The events following that act lead to more chaos, blood, and war: "A swift blessing may soon return to this our suffering country, under a hand accursed" (Macbeth, Act 3, Scene 6, ll. 53-55). Shakespeare clearly demonstrates the problems with feudalism.
In the end, Macbeth portrays the decline of feudalism and the rise of greater centralization as a welcomed change. Shakespeare usually includes and comments on the historical events occurring around the times in which his plays are set. 11th-century Scotland was experiencing a transition from the Age of Feudalism to the Age of Kings, as powerful lords gained increasing amounts of lands and "began to strengthen their control over their own lands" (W.H, Section 10-3, pp. 233). In Macbeth, the form of government is in practice completely feudal, yet the first hints of impending change begin to appear. Duncan is constantly referred to as 'King of Scotland' rather than as a lord, and the crown is inherited by birthright: "Our eldest, Malcolm, [...] we name hereafter the Prince of Cumberland" (Macbeth, Act 1, Scene 4, ll. 44-45). The great fortified castles of Scotland, the seats of power of Duncan and his nobles, show centralization at a small level, possibly implying the future strength of kings. Yet the most obvious example of historical foreshadowing is the final speech made by Malcolm as he regains the throne. He gives the Thanes a new title - that of Earls, "the first that ever Scotland in such an honor named" (Macbeth, Act 5, Scene 8, ll. 72-88). This change symbolizes the dawn of a new era of royal power and central government.
Plainly, Macbeth portrays the feudal world predominant in Europe, stressing its weaknesses, and foreshadows the historical transfer of power from feudal lords to kings. In fact, most of the play is either historical or political. England's King James I strongly supported Shakespeare, and he claimed he was a descendant of Banquo. Therefore, although the historical Macbeth was a noble and just ruler, in Shakespeare's play he is depicted as an ambitious and ruthless tyrant, while Banquo is humble and modest. Clearly, William Shakespeare wrote many plays with historical meaning behind them, naturally affected by his ideas or opinions. Macbeth is one of them.
** References refer to the Folger Library edition of 'Macbeth', the primary source book 'Sources of Western Civilization', and the book 'World History: Perspectives On The Past'.