What are the qualification criteria for the FIVB Club World Championship (both male and female)? For example, how was it decided which clubs competed in the 2016 male tournament played in Betim and the 2016 female tournament played in Manila?
Quoting from the Wikipedia page for the Men's Club World Championship:
The current format of the tournament involves eight teams competing for the title at venues within the host nation over a period of about one week; the winners of that year's AVC Club Volleyball Championship (Asia), African Clubs Championship (Africa), South American Volleyball Club Championship (South America) and CEV Champions League (Europe), along with the host city's team and a nominated team from North America. The amount of teams is increased through wild card invitees.
The women's tournament is the same.