Final answer:
The Tang Dynasty employed a professional army with aristocratic cavalry and peasant infantry, but notably, by the 750s, they increasingly relied on nomadic peoples like the Uyghurs for military support.
Step-by-step explanation:
The Tang Dynasty rulers often employed soldiers from various backgrounds to support their military campaigns and to maintain the empire's power. Primarily, they relied on a large professional army which included a core of aristocratic cavalry and a substantial peasant infantry. However, by the 750s, Tang frontier units increasingly adopted the strategy of utilizing pastoral, nomadic peoples from the steppes, such as the Uyghurs, as their prime military force. The involvement of these nomadic groups played a crucial role in the Tang military, especially in its campaigns to expand and secure the vast empire's frontiers across central Asia.