geographic rather than formal political areas, there were initially 13 zhōu and roughly 100 jun. Jin dynasty and the Southern and Northern Dynasties China was greatly divided during the following five centuries, during the Jin and Northern and Southern Dynasties period. The number of administrative units drastically increased due to intense warfare, fluid political boundaries, forced migrations, widespread population loss, and the loss of central government control in many areas particularly during the Sixteen Kingdoms. Although the legacy three-tier system was still in formal effect, rulers of various kingdoms had defined and re-defined provinces until they became increasingly sub-divided, blurring the distinction between provinces (zhou) and commanderies (jun) and reflecting the chaos of China at the time. Sui and Tang dynasties China was finally re-united by Emperor Wen of the Sui (581–618) in 589. As there were already over 100 provinces, the province and commandery levels of the administration were merged into one level, typically rendered in English as prefecture, marking the end of the commandery. Some Emperors preferred "jun" to refer to this level of administration, but most used "zhou" and the political function was the same, regardless. By the end of the Tang Dynasty the term jun saw no more use in China (and a new higher tier of administrative unit, the circuit (dao) had been introduced, bringing back a three-tier system). Taiwan (1920–1945) During 1920–1945, when Taiwan was under Japanese rule, there were divisions called 郡 (Mandarin: jùn, Japanese: gun). They are based on the Districts of Japan (郡 gun), which in turn were based on ancient Chinese jùn. Their officers were known as 郡守 (Mandarin: jùnshǒu, Japanese: gunshu). This was the title of ancient administrators of the Chinese jun (see below), and had never existed in Japan. By the end of 1945, there were 51 jun/kun in Taiwan. Administrative hierarchy In the Warring States period, the chief administrative officers of the areas were known as jun administrators (, , literally "defender of the jun"). In the Han dynasty, the position of junshou was renamed grand administrator (, . "Grand Defender"). Both terms are also translated as "governor". A grand administrator drew an annual salary of 2,000 dan () of grain according to the pinzhi (, pǐnzhì) system of administrative rank. Many former grand administrators were promoted to the posts of the Three Ducal Ministers or Nine Ministers later in their careers. Other uses In contemporary Chinese