Why is macbeth involved in an external conflict with banquo? In what way does macbeth fail to resolve this conflict

Macbeth gets greedy and believed that Banquo stole the throne that was supposed to be his when the prophecy said that it was Banquo’s children who will eventually have the throne. Macbeth planned to have Banquo and his son killed so they have no chance of taking the throne but Macbeth failed to resolve this because the Banquo’s son escaped and Banquo was the only one who’s killed.