Complex sentence: Their army, dubbed by historians'The Host of the Two Kings', numbered 55,000, five thousand of them mounted knights, while the Targaryens had only 10,000 men, many of uncertain loyalty and reliability.
Split into simpler sentences: Their army, dubbed by historians'The Host of the Two Kings', numbered 55,000, fully five thousand of them mounted knights. The Targaryen host in contrast only numbered 10,000 men, many of uncertain loyalty and reliability.