Which early civilization had a well organized unified empire with an elaborate system?

Incas is the early civilization which had a well organized, unified with an elaborate system. The inca civilization succeeded in prehistoric peru in the middle of c. 1400 and 1533 CE and their empire in due course prolonged cross ways western south america from quito in the north to santiago in the south creating it the largest empire ever seen in the americas and the largest in the world at that time. Fearless by the every so often harsh andean environment the incas occupied people and oppressed landscapes in such varied locations as plains, mountains, deserts, jungle and tropical rain forest.