After each Season, the progress of all players (not just in the division, but the pool of all players currently playing with leaderboard unlocked) will be put side-by-side, and compared. If your progress is:
- in the top 50 players on the world - you will be promoted to Championship League
- in the top 10% of the players - you will be promoted to Diamond League,
- in the top 20% - you will be promoted to Platinum League,
- in the top 30% - you will be promoted to Gold League
- rest of the players will be put in Silver League
Also worth noting is that divisions are populated automatically, in pools of 50 people, and after the threshold has been reached, new division is created. Every Season end will shuffle players between divisions, and you'll compete against those 49 people until the next Season end.