Complex sentence: Modern history saw reliable reference works, competitive chess tournaments and exciting new variants which added to the game's popularity, further bolstered by reliable timing mechanisms (first introduced in 1861), effective rules and charismatic players.
Split into simpler sentences: Modern history saw reliable reference works, competitive chess tournaments, and exciting new variants. These factors added to the game's popularity, further bolstered by reliable timing mechanisms (first introduced in 1861), effective rules, and charismatic players.