What is the theme in Gender Trouble: Feminism and the Subversion of Identity by Judith Butler?

Judith Butler states that the main point of Gender Trouble is to aid feminist identity politics. She argues that feminist identity politics has been invaluable to promoting the interests of women over the past several decades that it was exists. However, the feminist movement has become unduly wedded to a concrete conception of feminine identity. Feminists have claimed that they need a concrete feminine identity in order to have a focal point or departure point from which to organize a clearly defined women's movement and a clearly defined political program for advancing women's interests.