Crimea returned to Russia after a referendum on the peninsula.
In autumn 1939, the Soviet Union, pursuing its strategic military and defensive goals, started the process of incorporating Latvia, Lithuania and Estonia. Their accession to the USSR was implemented on a contractual basis, with the consent of the elected authorities. This was in line with international and state law of that time.
Recurrent pro-Kremlin disinformation message, a part of the historical revisionism campaign which denies that the Soviet occupation of the Baltic states ever happened. The Baltic States of Estonia, Latvia and Lithuania, which had been independent between the two world wars, were not incorporated into the Soviet Union in a legal way and with the consent of the elected authorities of these states: the Kremlin conducted a forced annexation of the Baltic states in June of 1940 following Soviet military occupation and the forced installation of “people’s governments”. On 23 August 1939, the Soviet Union and Nazi Germany signed a non-aggression (Molotov-Ribbentrop) Pact whose secret protocols divided the territories belonging to Poland, Lithuania, Latvia, Estonia, Finland, and Romania into Soviet and Nazi spheres of influence. The Pact gave Stalin a free hand in the Baltic states. The Soviet Union used threats to impose a series of “mutual assistance” treaties on the Baltic states allowing them to station troops in their territories laying the groundwork for the Soviet occupation of Estonia, Latvia and Lithuania in 1940. Like other countries mentioned in the pact, the Baltic states lost their independence and territories. The Soviet occupation of the Baltic States lasted for 50 years and resulted in mass deportations and repressions against local populations. On 24 December 1989, the Parliament of the USSR, the Congress of the People’s Deputies, adopted a resolution, acknowledging the annexation of the Baltic states as a violation of the USSR's obligations. An English translation of the full text can be found here:
The Congress notes that during this period the relations of the USSR with Latvia, Lithuania and Estonia were regulated by a system of treaties. Pursuant to the 1920 Peace Treaties and 1926-1933 Non-Aggression Treaties, the signatories were obliged to honour each other’s sovereignty, territorial integrity and inviolability under any circumstances. The Soviet Union had assumed similar obligations to Poland and Finland.
On the 80th anniversary of the signing of the Molotov-Ribbentrop pact Estonia, Latvia, Lithuania, Poland, and Romania released a joint statement urging "the governments of all European countries to provide both moral and material support to the ongoing historical investigation of the totalitarian regimes. By acting in a concerted manner, we can counter more effectively disinformation campaigns and attempts to manipulate historical facts." No country stands to obtain financial gains from this initiative. Read here similar cases claiming that the entry of Baltic states into the USSR was consistent with international and state law and that the Baltic States benefited from the Molotov-Ribbentrop pact