Complex sentence: In 1988, HBO's subscriber base expanded greatly as a result of the Writers Guild of America strike that year, as the channel had new programming in its inventory during a period in which the broadcast networks were only able to air reruns of their shows.
Split into simpler sentences: In 1988, HBO's subscriber base expanded greatly as a result of the Writers Guild of America strike that year. HBO had new programming in its inventory, while the broadcast networks were only able to air reruns of their shows.