WELLINGTON - Ms Jacinda Ardern promised “relentless positivity” as New Zealand’s prime minister, but in announcing her shock resignation on Thursday admitted the unrelenting demands of the job had finally worn her down. A fresh-faced Ms Ardern was elected prime minister in 2017, and in a tumultuous first term faced New Zealand’s worst terror attack, a deadly volcanic eruption, and the Covid-19 pandemic. Just 37 years old at the time, she became the country’s youngest prime minister since 1856 and a global icon for progressive politics. Ms Ardern won a landslide second term in 2020, but her popularity has been...