Cao Cao then attacked the Yellow Turban rebels at Shouzhang but failed to defeat them. After that, Cao Cao reformed his army, enforced military rules more strictly, and used incentives to encourage his men. He recognized that the rebels did not have a stable flow of supplies, as they relied on plundering to sustain themselves. Hence, Cao Cao launched surprise attacks on the rebels, prevented them from pillaging, and achieving ultimate victory and forcing the rebels to retreat north. Cao Cao pursued the rebels and defeated them again at Jibei (south of present-day Changqing District, Shandong). The rebels, numbering more than 300,000, including 100,000 civilians, surrendered to Cao Cao. Cao reorganized the surrendered troops to form the Qingzhou Corps (), while implementing the "tuntian" system for the people to provide for themselves and the military.