September 21 http://en.wikipedia.org/wiki/International_Day_of_Peace
The Gandhi Tour in support of International Day of Peace 2010
The International Day of Peace ("Peace Day") provides an opportunity for individuals, organizations and nations to create practical acts of peace on a shared date. It was established by United Nations resolution in 1981 to coincide with the opening of the General Assembly. The first Peace Day was celebrated in September 1982. In 2001 the General Assembly officially declared September 21 as the permanent date for the International Day of Peace.