Moscow abandoned its main bastion in northeastern Ukraine on Saturday, in a sudden collapse of one of the war's principal front lines after Ukrainian forces made a rapid advance. The swift fall of Izium in Kharkiv province was Moscow's worst defeat since its troops were forced back from the capital Kyiv in March. This could prove a decisive turning point in the 6-month-old war, with thousands of Russian soldiers abandoning ammunition stockpiles and equipment as they fled.