Complex sentence: The slavers of Yunkai are known as the Wise Masters and because of the cities lack of Unsullied they keep a mixed professional and slave army of approximately 4,000 with at least 1,000 mercenaries.
Split into simpler sentences: The slavers of Yunkai are known as the Wise Masters. Due to the city's lack of Unsullied, they rely on a mixed professional and slave army of approximately 4,000 with at least 1,000 mercenaries.