Liu Tsung-yüan was born in the eighth year of the Ta-li era of Emperor Tai-tsung of the T'ang dynasty, most of which fell within the year a.d. 773. The year itself was not one of major historical significance, but the period around Liu's birth saw the most drastic changes and the most serious turmoil T'ang China had ever experienced. The catalyst of these changes was the An Lu-shan rebellion, which broke out in 755 and ended in 763. After this rebellion China became a politically divided land. The military and political forces supporting An Lu-shan and his followers continued to rule the northeastern provinces, where the rebellion had originated. Many regional military commanders in the rest of China who had gained power during the court's effort to put down the rebellion, on the other hand, started asserting semi-independent status. These two combined factors greatly weakened the central government and resulted in almost incessant military revolts or threats of revolt. On the social level, the rebellion dealt a grave blow to the prestigious Shan-tung aristocracy, whose principal base, the Lo-yang area, was destroyed, accelerating the overall decline of the aristocratic class, a process that changed the fabric of Chinese society forever. In addition, the devastation of the north by continuous fighting complemented the rise of the southeast as the national economic center, and this marked a fundamental shift in China's economic and social geography.