The Xia dynasty is generally accepted as the first Chinese dynasty, established in the Yellow River valley around 2070 BCE. The Shang dynasty followed, lasting until 1046 BCE. The Zhou dynasty was the longest-lasting dynasty in ancient China, reigning from 1046 BCE until 256 BCE. After the fall of the Zhou dynasty, China entered the Warring States period, a time of conflict between various states that lasted until 221 BCE. In 221 BCE, the state of Qin emerged victorious from the Warring States period and established the Qin dynasty, the first unified empire of China.