Complex sentence: Taizong is typically considered to be one of the greatest emperors in China's history and henceforth, Emperor Taizong's reign was regarded as the exemplary model against which all other emperors were measured.
Split into simpler sentences: Taizong is typically considered as one of the greatest emperors in Chinese history. Throughout the rest of Chinese history, Emperor Taizong's reign was regarded as the exemplary model against which all other emperors were measured.