was macbeth destined to become king or did he force his way into this position because of the witches prophecy?

He totally forced his way into the crown. Macbeth was not in line for the throne. Malcolm (first) and then Donalbain (second) would have been in line first. With both sons getting the hell out of there to avoid being blamed for Duncan's murder, Macbeth went about his killing spree. It of course started with killing Duncan but extended to Banquo, Macduff's family....Macbeth was paranoid in the extreme so at any hint of danger to his kingship, he would impulsively lash out to protect it. He also retuned to the witches a second time so they could mess with his head even more.