The fall of the Han dynasty was followed by an age of fragmentation and several centuries of disunity amid warfare among rival kingdoms. During this time, areas of northern China were overrun by various non-Han nomadic peoples, which came to establish kingdoms of their own, the most successful of which was Northern Wei (established by the Xianbei). Starting from this period, the native population of China proper began to be referred to as Hanren, or the "People of Han", to distinguish them from the nomads from the steppe. Warfare and invasion led to one of the first great migrations of Han populations in history, as they fled south to the Yangzi and beyond, shifting the Chinese demographic center and speeding up sinicization of the far south. At the same time most of the nomads in northern China came to be sinicized as they ruled over large Chinese populations and adopted elements of their culture and administration. Of note, the Xianbei rulers of Northern Wei ordered a policy of systematic sinicization, adopting Han surnames, institutions, and culture.