We often forget that the USSR was the partner of Nazi Germany in 1940.
//On August 24, 1939, the Soviet Union and Nazi Germany signed a 10-year non-aggression treaty, called the Molotov-Ribbentrop pact. The pact contained a secret protocol, revealed only after Germany's defeat in 1945, according to which the states of Northern and Eastern Europe were divided into German and Soviet "spheres of influence". The secret protocol placed the Romanian province of Bessarabia in the Soviet "sphere of influence." Thereafter, both the Soviet Union and Germany invaded their respective portions of Poland, while the Soviet Union occupied and annexed Lithuania, Estonia and Latvia in June 1940, and waged war upon Finland (1939–1940).
On June 26, four days after France sued for an armistice with the Third Reich, the Soviet Union issued an ultimatum to Romania, demanding the latter to cede Bessarabia and Bukovina. After the Soviets agreed with Germany that they would limit their claims in Bukovina, which was outside the Molotov-Ribbentrop Pact's secret protocols, to northern Bukovina, Germany urged Romania to accept the ultimatum, which Romania did two days later. The Moldavian Soviet Socialist Republic was thereafter created following the entrance of Soviet troops on June 28, 1940.