Complex sentence: He became politically active in the late 1960s when he was a student at Alberto Masferrer School, but he was not part of any political organization until he was introduced to the Unified Popular Action Front (FUAR or Frente Unido de Accion Revolucionaria).
Split into simpler sentences: He became politically active in the late 1960s when he was a student at Alberto Masferrer School. He was not part of any political organization until he was introduced to the Unified Popular Action Front (FUAR or Frente Unido de Accion Revolucionaria).