it is unfair to claim that the two-day visit to Moscow of Nazi Foreign Minister Ribbentrop was the main reason for the start of the Second World War.
In autumn 1939, the Soviet Union, pursuing its strategic military and defensive goals, started the process 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.
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 Baltic States were not beneficiaries of the Molotov-Ribbentrop pact. Like other countries mentioned in the pact, they lost their independence and territories. 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.
See similar disinformation narratives on this issue - The Baltic states benefited from the Molotov-Ribbentrop Pact; The Baltic states are perpetuating the myth of the Soviet occupation and The Baltic states refuse to celebrate the victory over fascism.