Complex sentence: With the war escalating, the club's own players were not able to play as much for Blackpool and Blackburn Rovers decided to play in the league which meant that their players who had played for Blackpool the previous season would no longer be available.
Split into simpler sentences: With the war escalating, the club's own players were not able to play as much for Blackpool. In addition, Blackburn Rovers decided to play in the league which meant that their players, who had played for Blackpool the previous season, would no longer be available.