What was the incas greatest contribution and why

The Inca’s greatest contribution (to civilization) is their organizational abilities and the federalism that they fostered during their short period of influence. Inca rulers developed a federation wherein adjacent societies that operated in a pattern of up and down, joined political, cultural and social groups to form a bigger federation of many societies. The ancient Peru (between 1400 and 1533 CE), was flourished due to Inca civilization. This made the empire extended across the western South America from Quito in the north to Santiago in the south hence, making the empire the largest in the Americas and the largest in the world during that time.  

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