By the mid-20th century, "Chicano" began to be used to reference those who resisted total assimilation, while "Pocho" referred (often pejoratively) to those who strongly advocated for assimilation. In his essay "Chicanismo" in "The Oxford Encyclopedia of Mesoamerican Cultures" (2002), José Cuéllar, dates the transition from derisive to positive to the late 1950s, with increasing usage by young Mexican-American high school students. These younger, politically aware, Mexican Americans adopted the term "as an act of political defiance and ethnic pride," similar to the reclamation of "Black" by African Americans. The Chicano Movement of the 1960s and early 1970s furthered the reclamation process of "Chicana/o", challenging those who used as a term of derision on both sides of the Mexico-U.S. border.