21 September: International Day of Peace

The International Day of Peace (“Peace Day”) is observed around the world each year on 21 September. Established in 1981 by unanimous United Nations resolution 36/37, the General Assembly has declared this as a day devoted to “commemorating and strengthening the ideals of peace both within and among all nations and peoples.” 
Furthering the Day’s mission, the General Assembly augmented the original resolution in 2001, fixing the date on 21 September. For the text of this second unanimous UN resolution, Peace Day provides a globally shared date for all humanity to commit to Peace above all differences and to contribute to building a Culture of Peace.

History:

21 September 1982 was the first occurrence of the International Day of Peace. The theme of the first International Day of Peace was the Right to peace of people.

In 2001 the opening day of the General Assembly was scheduled for 11 September, and Secretary General Kofi Annan drafted a message recognising the observance of International Peace Day on 21 September. That year the day was changed from the third Tuesday to specifically the twenty-first day of September, to take effect in 2002.
A new resolution was passed by the General Assembly,sponsored by the United Kingdom  and Costa Rica , to give the International Day of Peace a fixed calendar date, 21 September, and declare it also as a day of global ceasefire and non-violence