Complex sentence: After defeating the previously dominant Yuezhi in the 2nd century BC, Xiongnu became a dominant power on the steppes of eastern Asia and have ruled southern Siberia, Mongolia, western Manchuria, and the Chinese provinces of Inner Mongolia, Gansu and Xinjiang.
Split into simpler sentences: After defeating the previously dominant Yuezhi in the 2nd century BC, Xiongnu became a dominant power on the steppes of eastern Asia. They were active in southern Siberia, Mongolia, western Manchuria, and the Chinese provinces of Inner Mongolia, Gansu and Xinjiang.