Immediately following King Duncan's assassination, chaos ensues throughout the country as Duncan's sons flee to England and Ireland and high-ranking officials become suspicious and cautious. After Macbeth becomes King of Scotland, he rules as a bloodthirsty tyrant, who is willing to murder anyone he considers a threat to his authority. A conversation between Lennox and a Scottish Lord following Duncan's assassination provides insight into the hostile environment of Scotland under Macbeth's tyrannical reign. The Lord tells Lennox,

"Thither Macduff Is gone to pray the holy king upon his aid To wake Northumberland and warlike Siward, That by the help of these—with Him above To ratify the work—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 honors" (Shakespeare, 3.6.30-36).

The Lord's description of their country presents a grim picture of Scotland, where the citizens do not have enough food, cannot rest at night, and fear for their lives. Lennox responds by saying that their country is "suffering country Under a hand accursed!," which emphasizes the destructive, hostile environment in Scotland under Macbeth's reign. In act 4, scene 3, Macduff petitions Malcolm to return to Scotland in order to reclaim his rightful throne and restore their country to its former glory. Macduff also paints a depressing view of Scotland under Macbeth by telling Malcolm,

"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 yelled out Like syllable of dolor" (Shakespeare, 4.3.4-8).

Overall, one can assume that Scotland has turned into a dangerous country, where citizens live in perpetual fear and suffer under Macbeth's tyranny following King Duncan's assassination.

Immediately after King Duncan's death, the entire castle erupts into a flurry of emotion and horror. Since these responses are personal and anecdotal, it can be difficult to discern how the death of King Duncan affects the country. In order to find out how the entire country is affected, it is helpful to look at Act 4, scene 3 and the exchanges between Malcolm and Macduff. 

In Act 4, scene 3, Macduff describes the state of the nation:

MACDUFF: Each new morn / New windows howl, new orphans cry, new sorrows / Strike heaven on the face, that it resounds / As it felt with Scotland, and yelled out / Like syllable of dolor. (IV.iii.5-9)

Macduff has been shown to be a trustworthy character within the play, so his descriptions can be believed. It appears that Scotland has fallen apart with the death of King Duncan. The fighting has killed many of the men in the country and created "new orphans." Macduff describes Scotland as a soldier straddling a fallen comrade while also fighting the comrade's attackers ("Let us rather / Hold fast the mortal sword and, like good men, / Bestride our downfall'n birthdom," IV.iii.3-4). This image can be helpful when trying to imagine Scotland after Duncan's death.