When a terrorist massacred 50 people at two New Zealand mosques last week, Prime Minister Jacinda Ardern immediately grasped the nettle. "I can tell you one thing right now," she told the media. "Our gun laws will change."

That's what effective leadership looks like. New Zealand's Cabinet has now agreed in principle to overhaul those laws, experts are reviewing ways to make the country safer from firearms and, Ms Ardern promised, "within 10 days of this horrific act of terrorism, we will have announced reforms".