Editor’s Note: This is a heavily revised and updated version of an article written by the authors for these pages in 2016. Don’t miss our comprehensive guide to Russia’s war against Ukraine.    A press conference with U.K. Prime Minister Boris Johnson captivated the world when Daria Kaleniuk, a Ukrainian activist, implored him and other Western leaders to set up a no-fly zone over Ukraine to shelter its people from Russian aircraft. The tragedy of the current situation, the sincerity and sadness of the activist, and prime minister’s delicately worded but practical response — in which he told her that there would … Continue reading The Dangerous Allure of the No-Fly Zone