Here is a short list of things to think about:
1. The well-loved King Hamlet has died and his brother, Claudius, has taken the throne.
2. Claudius has also married his widowed sister-in-law, Gertrude, which many consider an incestuous relationship.
3. Young Fortinbras of Norway is planning an attack on Denmark to regain lands his father lost to Denmark many years ago. He is doing this with mercenaries and without his King's knowledge.
4. There is a ghost visiting the castle.
5. The ghost is that of King Hamlet, and he is coming to reveal that he was in fact murdered by Claudius.
6. Polonius has ordered Ophelia to stop seeing Hamlet. He is also using her to set-up Hamlet to discover what is wrong with him.
7. Polonius and Claudius are spying on Hamlet.
8. Hamlet's friends Rosencrantz and Guildenstern have been summoned by the king and queen in order to spy on Hamlet.
9. Hamlet knows he should take revenge on Claudius but seems thwarted at every turn.
10. Hamlet accidently murderes Polonius -- causing true madness in Ophelia and a blood-thirsty need for vengence in Laertes.
11. Hamlet is sent to England to be put to death there under order by King Claudius.
12. Ophelia commits suicide.
13. Leartes and Claudius plot Hamlet's murder.
14. Their murder plot goes slightly awry when Gertrude accidently drinks the poisoned cup meant for Hamlet.
15. Laertes does land a poisoned strike on Hamlet, but Hamlet returns the favor and kills Laertes and Claudius with the same poisoned sword.
16. Fortinbras arrives in the final scene to take the crown of Denmark -- thus leaving Denmark in the hands of a foreign leader.
As you can see every single plot event of the play is a sign of the things that are not well in the state of Denmark. As Hamlet says in Act 1, it is "an unweeded garden" and there seems to be no chance in restoring the kingdom to its former glory. All of the principle characters are dead by the end of the play.