The Soviet Union, which did not recognize the sovereignty of Romania over Bessarabia since the union of 1918, issued an ultimatum on 28 June 1940 demanding the evacuation of the Romanian military and administration from the territory it contested as well as from the northern part of the Romanian province of Bukovina. Under pressure from Moscow and Berlin, the Romanian administration and armed forces retreated to avoid war. Adolf Hitler used Soviet occupation of Bessarabia as justification for German occupation of Yugoslavia and Greece and German attack on USSR.