You would use a semicolon (;) when you could stop a sentence but choose to continue it further.
Answer
Macbeth is not at peace because, in order to become a king, he murdered the previous king, Duncan. Not only does this murder make Macbeth consumed with guilt, but it triggers a series of events that make him feel more and more uneasy. Macbeth later murders Banquo, convinced that he also represents a threat to his power, while Duncan's son plots a revenge against Macbeth.
