How did Philip Noel Baker win the Nobel Peace Prize?

Philip Noel-Baker in 1959 won the Nobel Peace Prize for his hard and dedicating work to end WWII (World War 2.) He wrote and signed a charter written in (San Francisco, USA) that basically ended WWII.

http://www.nobelprize.org/nobel_prizes/peace/laureates/1959/noel-baker-bio.html