Complex sentence: Although the PrHL lasted only two seasons, minor-pro and junior league hockey thrived in the west for many years thereafter, eventually coalescing into the major junior Western Hockey League in 1966.
Split into simpler sentences: Although the PrHL lasted only two seasons, minor-pro and junior league hockey thrived in the west for many years thereafter. The junior leagues eventually coalesced into the major junior Western Hockey League in 1966.