UN remembrance and reconciliation DAY
UN remembrance and reconciliation DAY is held on May 9. 8–9 May. This event in the first decade of the month May is annual. 
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By resolution 59/26 of 22 November 2004, the UN General Assembly declared 8–9 May as a time of remembrance and reconciliation and, while recognizing that Member States may have individual days of victory, liberation and commemoration, invited all Member States, organizations of the United Nations System, non-governmental organizations and individuals to observe annually either one or both of these days in an appropriate manner to pay tribute to all victims of the Second World War.
The Assembly stressed that this historic event established the conditions for the creation of the United Nations, designed to save succeeding generations from the scourge of war.
Source: un.org
However, resolutions alone ("surprisingly"), as it turned out, cannot prevent this.
Similar holidays and events, festivals and interesting facts
Day of Homage to the Spanish deported and deceased in Mauthausen and other camps and to all victims of Nazism in Spain on May 5
Lost Sock Memorial Day on May 9
Rasta/Bob Marley Day on May 11
Day of Remembrance of Ukrainians Who Saved Jews on May 14
B. B. King Day on May 14
Peace Officers Memorial Day on May 15 (United States);
Nakba Day in the State of Palestine on May 15 (Day of Remembrance for Palestine Refugees)