Complex sentence: The oldest is the Pearly Guild, which began in 1902; modern additions include the London Pearly Kings and Queens Society which started in 2001 following a disagreement, another is the Pearly Kings and Queens Guild.
Split into simpler sentences: The oldest is the Pearly Guild, which began in 1902. Modern additions include the London Pearly Kings and Queens Society, which started in 2001 following a disagreement, and the Pearly Kings and Queens Guild.