Complex sentence: The History Channel broadcast five nights of documentaries featuring the Roman Empire, which were hosted by Stevenson, McKidd, and Varma, a collaboration which was the first of its kind between the two networks.
Split into simpler sentences: The History Channel broadcast five nights of documentaries featuring the Roman Empire, which were hosted by Stevenson, McKidd, and Varma. This collaboration was the first of its kind between the two networks.