Complex sentence: He is a member of Convergència Democràtica de Catalunya (CDC) and founder of the Joventut Nacionalista de Catalunya, or Nationalist Youth of Catalonia, the youth sector of the CDC, of which he was secretary and president from 1986 to 1991.
Split into simpler sentences: He is a member of Convergència Democràtica de Catalunya (CDC). He was a founder of the Joventut Nacionalista de Catalunya, or Nationalist Youth of Catalonia, the youth sector of the CDC, of which he was secretary and president from 1986 to 1991.