 Complete the following phrase:  China emerged as one of the worlds first civilizations, in the fertile basin of the Yellow River in the North China Plain. China was one of the worlds foremost economic powers for most of the two millennia from the 1st until the 19th century. For millennia, Chinas political system was based on absolute hereditary monarchies, or dynasties, beginning with the Xia dynasty in 21st century BCE. Since then, China has expanded, fractured, and re-unified numerous times. In the 3rd century BCE, 