Can you please explain the civil war in the play, Macbeth?
In Shakespeare's Macbeth, there are really two civil wars: the play begins and ends with civil wars.
At the start of the play, Macdonwald and Cawdor, two Scottish thanes, are revolting against the ruling monarch, King Duncan. The two traitors are joined by an opportunistic monarch from another country, but he doesn't get much attention in the dialogue. Macbeth, Banquo, and Macduff, presumably, lead Duncan's forces in battle and defeat the traitors. Macbeth, especially, gains favor and fame and reputation for his prowess on the battlefield.
By the end of the play, Malcolm, Duncan's son, and Macduff, lead an army against Macbeth that consists of both Scottish and English forces. This battle, however, is very much over before it begins, since Macbeth's forces, for the most part, are no longer loyal to Macbeth. Macduff defeats Macbeth in one-on-one battle, and Malcolm's forces are victorious.
That the play's structure is encircled in wars is telling. This is a violent and bloody drama--from the description in Act 1 of Macbeth cutting Macdonwald from the navel to the jaw (in other words, he disemboweled him), to Macduff entering the stage carrying Macbeth's head in Act 5--violence and blood and the unnatural dominate this play.
The civil war that marks the beginning of The Tragedy of Macbeth is defined by rebellion and traitorous behavior against King Duncan. These events played out on the stage parallel the real-life rebellion and attempt on King James's life in 1605.
King James I of England was the reigning monarch at the time at which Shakespeare wrote Macbeth. The Gunpowder Plot was engineered by angry Catholics who decided to rebel against the Protestant King James and try to assassinate him. The plot did not succeed, but the treasonous behavior was enough to make the king extremely wary of his Catholic enemies from then on.
Many scholars believe that Shakespeare deliberately wrote in the civil war in Macbeth in order to reassure King James that the bad guys will always lose, and better yet, they will always be severely punished by the good guys. The rebels at the start of the play, Macdonwald and Cawdor, are indeed killed for their attempt to take down the rightful monarch, and the same happens to Macbeth at the end of the play.
The battle referred to in the opening scene of 'Macbeth' as 'the hurlyburly' is the civil war being fought in Duncan's Scotland. In act 1 sc.2 the bleeding sergeant informs the king how 'the merciless Macdonwald--worthy to be a rebel' was being assisted by the Irish foot-soldiers in his war against the king's men. It was Duncan's general, Macbeth, who faced the slavish Macdonwald with 'his brandish'd steel' and killed him in that instant. Later in the same scene, Ross reported how the Thane of Cawdor proved himself the 'most disloyal traitor' who was again dealt with most conclusively by 'that Bellona's bridegroom', Macbeth. Thus from the very beginning, Duncan's Scotland was severely disturbed by civil wars.
Ever since Macbeth usurped the throne by killing Duncan, secret killings and conspiracies persisted in Scotland. When the English army led by Malcolm and Macduff came to oust the tyrant Macbeth, almost all the Scottish nobles defected Macbeth to join the army. The outcome was another civil war in which Macbeth was defeated at the battle of Dunsinane. This civil war led to the coronation of Malcolm as the lawful king of Scotland.