A is for Alpha Cygnus IX, where Sarek of Vulcan once concluded an historic treaty.
B is for Betazoid wedding ceremonies. The wedding party is naked. Saves on expensive dresses and tuxedos.
C is for the Cardassian-Federation War of the 2350s and 2360s.
D is for dilithium miners. You'd think that they could afford nicer digs (pun intended).