To answer this question, look first at Act IV, Scene II, and the conversation between Ross and Lady Macduff. As Ross defends Macduff's sudden departure, for instance, he says to Lady Macduff:
But cruel are the times when we are traitors
And do not know ourselves; when we hold rumor
From what we fear, yet know not what we fear.
In other words, under Macbeth, Scotland has become a place of uncertainty. Moreover, loyal men like Macduff are denounced as traitors, even though they have not committed an act of treason. As a result, families are broken up, wives left without husbands, and children left without fathers. There is an immense danger, too, as we see from the brutal murder of Lady Macduff and her son later in this scene.
This notion is also reinforced in the next scene when Malcolm calls Macbeth a "tyrant" and talks of "poor Scotland."
Under Macbeth, then, Scotland has deteriorated from a kingdom of stability to one of extreme violence and oppression.
Under Macbeth's rule, Scotland changed for the worse. Macbeth killed the good old king Duncan, and Duncan's sons, Malcolm & Donalbin, escaped to England & Ireland respectively for their safety. Constantly suffering from a guilty conscience & a deep psychological fear, Macbeth proves to be a cruel, tyrannical king, haunted by the prophecy that Banquo's issues would be the future kings. Murderers appointed by him kill Banquo & attempt to kill Banquo's son, Fleance. Subsequently, Macbeth gets the family of Macduff killed. As Macbeth moves from fear to fear, he unleashes a reign of terror in Scotland, killing wholesale whomsoever he doubts to be his enemy and therefore, a traitor.
In act3 sc.6, a Lord, while in conversation with Lennox, refers to Macduff's visit to the court of the English king to initiate a military campaign against Macbeth so that life returns to normal: '.......we may again / Give to our tables meat, sleep to our nights, / Free from our feasts and banquets bloody knives, / Do faithful homage and receive free honours:/ All which we pine for now'.
Ross, talking to Lady Macduff in act4 sc.2, uses the analogy of a voyage to suggest the state of affairs in Scotland under Macbeth's rule: 'But cruel are the times, when we are traitors/ And do not know ourselves, when we hold rumour / From what we fear, yet know not what we fear, / But float upon a wild and violent sea / Each way and move'.
How Scotland changed under the despotic violence of Macbeth is best expressed in the Macduff-Macbeth conversation in act4 sc.3. We hear Macduff say, 'Each new morn / New widows howl, new orphans cry, new sorrows / Strike heaven on the face, that it resounds/ As if it felt with Scotland and yell'd out / Like syllables of dolour'. Malcolm responds in the similar vein of melancholy anguish:'I think our country sinks beneath the yoke;/ It weeps, it bleeds, and each new day a gash / Is added to her wounds...' Later in the same scene, Ross describes the deplorable state of Scotland in highly coloured language:
" It cannot
Be call'd our mother, but our grave; where nothing,
But who knows nothing, is once seen to smile;
Where sighs and groans and shrieks that rend the air
Are made, not mark'd; where violent sorrow seems
A modern ecstasy; the dead man's knell
Is there scarce ask'd for who; and good men's lives
Expire before the flowers in their caps,
Dying or ere they sicken".
When the play begins, Scotland, with no little thanks to MacBeth and Banquo is victorious in battle, first against Macdonwald and the Irish soldiers and then against the Norwegian King. King Duncan and all of Scotland is feeling strong and secure. With each murder Macbeth commits, Scotland is reduced both in strength and security. By act IV, there is much fighting with the country itself, and Malcom and Donalbain have had to reach outside Scotland for help in bringing Macbeth down. There is distrust everywhere; even MacDuff's wife accueses her husband of being a traitor because she believes he as run off. By the end of the play, we see that Macbeth has reduced the once stable country to ruin and chaos, a condition that can only be rectified by Macbeth's death.