Why is the Nobel Peace Prize award and for what?

Why: The Prize rewards individuals or associations who 'shall have done the most or the best work for brotherhood between nations, the abolition or reduction of standing armies and for the holding and promotion of peace congresses'. 

For what: It has been awarded to 109 individuals and 28 organizations between 1901 and 2020. Some notable recipients include Martin Luther King Jr., Nelson Mandela, Mother Teresa, Desmond Tutu, and the United Nations. The Prize is usually awarded in Oslo, Norway, on December 10, the anniversary of Alfred Nobel's death.