The Anti-Federation League was a group of individuals who were set against the United Federation of Planets, and are set against the ideals and methods of the Federation Starfleet. Believing that if Starfleet was primary an exploratory and diplomatic organization, then why should starships be equipped with mass arnaments and engage in battle with other species and empires.
In 2267, a group of League members led by a man named Alan, departed on a two-month cruise into Klingon space aboard the SS Harmony, in the hopes of achieving what Starfleet and the Federation couldn't do, and make peace with the Klingon Empire. Unfortunately, their efforts resulted in their ship being attacked and them being taken prisoner. Eventually, four of the six were rescued alive by a team from the USS Enterprise. (TOS novel: Demands of Honor).