This document provides information about various nomadic groups including the Xiongnu, Arabs, Masai, Turks, Mongols and compares their social and political structures to settled agricultural civilizations. It discusses how nomadic groups like the Mongols were able to conquer large empires, noting that they promoted merit-based promotion, had superior organization and tactics, and were able to unite tribes. The document also summarizes the Mongol conquests in China, Persia, and Russia, how the Yuan Dynasty changed Chinese political and social structures, and the factors that led to the decline of Mongol rule.