Complex sentence: The reasons for Brown's departure were never fully disclosed, but it started a downward spiral that continued for many years; indeed, Blackpool went on to spend the next 29 years in the lower two divisions of the Football League.
Split into simpler sentences: The reasons for Brown's departure were never fully explained, but it started a downward spiral that continued for many years. Indeed, Blackpool would go on to spend the next 29 years in the lower two divisions of the Football League.