From https://www.un.org/en/observances/end-racism-day
Background
The International Day for the Elimination of Racial Discrimination is observed annually on the day the police in Sharpeville, South Africa, opened fire and killed 69 people at a peaceful demonstration against apartheid “pass laws” in 1960.
In 1979, the General Assembly adopted a programme of activities to be undertaken during the second half of the Decade for Action to Combat Racism and Racial Discrimination. On that occasion, the General Assembly decided that a week of solidarity with the peoples struggling against racism and racial discrimination, beginning on 21 March, would be organized annually in all States.
Since then, the apartheid system in South Africa has been dismantled. Racist laws and practices have been abolished in many countries, and we have built an international framework for fighting racism, guided by the International Convention on the Elimination of Racial Discrimination. The Convention is now nearing universal ratification, yet still, in all regions, too many individuals, communities and societies suffer from the injustice and stigma that racism brings.