Until the 2015 World Cup this was mostly through having Full Membership of the ICC, and for the 2019 World Cup this was mostly through ranking position in the ICC ODI Championship.
Prior to the 2015 World Cup, teams' participation was largely influenced by their status as full members of the ICC. Conversely, for the 2019 World Cup, qualification was primarily driven by a team's performance in the ICC ODI Championship rankings.