In Act One, Scene 1, Horatio, Marcellus, and Bernardo discuss the appearance of the ghost of King Hamlet, the father of Prince Hamlet:
In what particular thought to work I know not,/But in the gross and scope of mine opinion,/This bodes some strange eruption to our state (I,i, 67-69)
Horatio worries that the King has been murdered since his ghost reappears. For one thing, the guards are worried about young Fortinbras of Norway seeking revenge for King Hamlet's slaying of his father; they fear that the son will want to reclaim lands lost by his father, Fortinbras.
Secondly, another eruption to the state is the possible reason for Hamlet's ghost: regicide. As a serious crime, regicide greatly disrupts the state, and the citizens become anxious as the possible disruption of the entire country can occur with the takeover of someone else. Horatio alludes to the "Disasters in the sun"(I,i,118) after the "mightiest Julius fell" (I,i,114)
Lastly, the guards are concerned about what the ghost will say to his son, Hamlet, and how the prince will react to what he is told. If Hamlet avenges his father's death, he may be killed, and no rightful heir will be in line for the throne. In addition, other conflicts may arise from Hamlet's action: Civil strife, wars outside Denmark, etc.
This scene, thus, introduces the motif of indirection and deception that prevails throughout Shakespeare's play, "Hamlet."
In Act I, Scene I, the guards are discussing the possible "eruptions" (problems) which might occur to the "state" (country) after the appearance of the former king's ghost. According to Horatio, the first of these is war with Norway. Horatio believes this is likely to happen since the late king conquered a number of Norwegian territories and the new king of Norway, Fortinbras the younger, is keen to retake them.
Secondly, Horatio believes that King Fortinbras will succeed in retaking his lost territories. This is because he believes that the appearance of their late king’s ghost is a bad omen which signals their impending defeat.
Finally, Horatio believes that Denmark will experience many more bad omens. To illustrate this point, he uses the former Roman emperor, Julius Caesar, as an example. Just before Caesar’s assassination, for example, it was said the Roman streets were filled with blood, corpses rose from their graves, and the moon almost disappeared from the sky. Horatio is worried that events like these will soon occur in Denmark.