political parties leaders

Earlier this week Prime Minister Scott Morrison called a late-night party room meeting to talk about leadership spills. It wasn't that Morrison had decided to save us all a lot of time by stepping down and letting the cabinet fight, Death of Stalin style, for his suddenly vacant seat -- quite the opposite. The rule changes shore up his position, by making it harder to knife a sitting prime minister.

So, given this happens so often, it's worth examining the rules. How do the major parties decide on who will lead them?