The women's division of professional wrestling has maintained a recognized world champion since 1937, when Mildred Burke won the original World Women's title. She then formed the World Women's Wrestling Association in the early 1950s and recognized herself as the first champion, although the championship would be vacated upon her retirement in 1956. The NWA, however, ceased to acknowledge Burke as their Women's World champion in 1954, and instead acknowledged June Byers as champion after a controversial finish to a high-profile match between Burke and Byers that year. Upon Byers' retirement in 1964, The Fabulous Moolah, who won a junior heavyweight version of the NWA World Women's Championship (the predecessor to the WWE's Women's Championship) in a tournament back in 1958, was recognized by most NWA promoters as champion by default.
What year did Mildred Burke retire? 
1956