  The Zoo solution to Fermi's Paradox proposes that extraterrestrial
intelligences (ETIs) have agreed to not contact the Earth. The strength of this
solution depends on the ability for ETIs to come to agreement, and
establish/police treaties as part of a so-called "Galactic Club". These
activities are principally limited by the causal connectivity of a civilisation
to its neighbours at its inception, i.e. whether it comes to prominence being
aware of other ETIs and any treaties or agreements in place.
  If even one civilisation is not causally connected to the other members of a
treaty, then they are free to operate beyond it and contact the Earth if
wished, which makes the Zoo solution "soft". We should therefore consider how
likely this scenario is, as this will give us a sense of the Zoo solution's
softness, or general validity.
  We implement a simple toy model of ETIs arising in a Galactic Habitable Zone,
and calculate the properties of the groups of culturally connected
civilisations established therein. We show that for most choices of
civilisation parameters, the number of culturally connected groups is greater
than 1, meaning that the Galaxy is composed of multiple Galactic Cliques rather
than a single Galactic Club. We find in our models for a single Galactic Club
to establish interstellar hegemony, the number of civilisations must be
relatively large, the mean civilisation lifetime must be several millions of
years, and the inter-arrival time between civilisations must be a few million
years or less.
