Smogon's World Cup of Pokemon involves teams composed of players from various different regions competing in various formats on Pokemon Showdown; this will resolve according to which team is listed as champion in the Smogon thread dedicated to the event. Recent winners include:

2024: US Midwest

2023: Spain (did not qualify)

2022: France

2021: US South

2020: Italy

The team rosters can be seen here, and information on the pools stage (including current standings and matchups) can be seen here. The eight teams I initially put as answers are not the only possible winners, as there are 20 teams in the main event; other contenders include India, Brazil, and Chile.