On August 23, 1939 the Molotov-Ribbentrop Pact was signed with secret protocols that divided Europe into German and Soviet spheres of interest.
The pact lead to the 1940 annexation of the Baltic countries by the Soviet Union, resulting in an occupation that lasted for 50 years until the collapse of the Soviet Union in 1991.
The European Commission ahead of the remembrance day issued a statement by First Vice-President Timmermans, Commissioner Jourová and Commissioner Navracsics.
"[The signing of the Molotov-Ribbentrop Pact] marked the beginning of one of the darkest periods in the recent history of our continent, bringing with it the deportation, torture and murder of tens of millions of people under totalitarian regimes," reads the statement.
"While the end of World War II marked the defeat of the Nazi regime, many Central and Eastern Europeans continued to suffer under other totalitarian regimes."
On Monday Latvia also marks the 27th anniversary of the Baltic Way demonstration in 1989.