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The historical changes of the Maowusu Desert can be divided into three phases:the late Tang dynasty phase,the Song-Yuan-Ming dynasty phase,and the late Ming dynasty to the present phase.Different parts of the desert were formed in different times,with the northwest part being the earliest to form.As all evidence shows,the Maowusu Desert in its early stage is believed to have taken shape largely around the ancient site of the You state during the years of Tianbao in the Tang dynasty,which is nowadays the east half of the Etuoke banner and Prior-Etuoke banner.The formation of the initial Maowusu Desert is not attributed to the so-called over-cultivation from farming but to the long-time exceedingly quartered husbandry starting from the 4th year of the Zhenguan to the years of Tianbao in the Tang dynasty,which resulted in the destruction of the ecology of the natural grassland.