In the immediate aftermath of the Christchurch mass shooting, New Zealand's Prime Minister Jacinda Arden had to address the nation in the throes of an unprecedented tragedy.

"Clearly what has happened here is an extraordinary act of violence," she said. "Many of those who will have been directly affected by this shooting may be migrants to New Zealand. They may even be refugees here. They have chosen to make New Zealand their home and it is their home. They are us. The person who has perpetuated this violence against us is not."

Not only did Ardern manage to unite the people of New Zealand after this horrible tragedy, six days later she passed sweeping gun reform, moving to ban military-style semi-automatic weapons, assault rifles and high-capacity magazines.

Historian Nancy Koehn said Ardern's response to the Christchurch shooting was a radical combination of emotional empathy and direct action. Koehn is an historian at the Harvard Business School, where she holds the James E. Robison chair of Business Administration, and her latest book is "Forged in Crisis: The Power of Courageous Leadership in Turbulent Times."

"The thing that so struck me ... about Jacinda Ardern, watching her, was how she combined emotional guidance and empathy and a voice for the nation and world reeling from this violence, with immediate, powerful, targeted action," Koehn told Boston Public Radio.

"Here is a leader who's very conscious of both the emotional responsibilities of a leader — to help a nation heal and come together and offer support for those very directly affected by this tragedy — and at the same time [saying], 'I've got to act,'" she said.