In 1940, during World War II, Romania agreed to an ultimatum and ceded Moldova to the Soviet Union, which organized it into the Moldavian SSR. In the middle of 1941, Romania joined Hitler's Axis in the invasion of the Soviet Union, recovering Bessarabia and northern Bukovina, as well as occupying the territory to the east of the Dniester it dubbed "Transnistria". By the end of World War II, the Soviet Union had reconquered all of the lost territories, reestablishing Soviet authority there. The Soviets strongly promoted the Moldovan ethnic identity, against other opinions that viewed all speakers of the Romanian language as part of a single ethnic group, taking advantage of the incomplete integration of Bessarabia into the interwar Romania.