I was reading 1491 by Charles C Mann and came across the chapter on the Inca where the author writes how it was one of the largest empires in the world, achieved great feats of architecture and technology, and seemed to have abundant storehouses. All of this without money.
I want to know more about their economic system. How did they achieve such efficiency? How were goods and services produced? How did they get people to do work like farm surplus food, serve in the army, labor to construct monuments? If all of this was done under the threat of violence, what prevented revolts and unrest from breaking out?
The Inca, like the many civilisations which preceded them, were a collectivist society. Droughts, El Niño events, harsh terrain and violent natural disasters forced the Andean people to live and think cooperatively, and so developed the value of the group over the individual. Collectivism is reflected in Andean artwork, which places emphasis on roles and actions over specific events and the particular individuals related to them. As a collectivist society, the Inca had a strong sense of national and cultural unity. Inca society was also predominantly based on strong kinship ties and a system of communal groups called ayllu. Each ayllu in the empire was a community defined by its territory and kinship relations. Each member of an ayllu was obligated to provide services for the community as a whole: labour, merchandise, food etc. These communal blood ties could be traced back many generations, and ensured social harmony.
Each ayllu was in turn obligated to provide labour and/or produce to the state, under the Inca taxation system called the mit'a. This meant that each ayllu had to coordinate its labour distribution by sending some members away to provide services to the state, while selecting others to perform the duties of those sent for mit'a service. When the Inca conquered new territories it was not difficult to persuade them to submit to the mit'a: the ayllu system was already a fundamental institution across the Andes, and to join the wider community (the state) was to ensure that the people would always have a safety net in times of drought, famine or other economic hardships. Submission was a small price to pay for stability. Some groups did resist submitting to the mit'a, but troublesome populations were dealt with by forcibly resettling them away from their homelands. These mitimaes, foreigners, allowed the Inca to assert social control across the empire by separating people from their ayllus, the very basis of their communal existence, and forcing them to live among strangers and away from their sacred sites and deities. They also relocated trusted, docile populations into newly conquered territory for the same purpose of social control. The same practices have been enforced by collectivist states in the modern era.
Essentially, the Inca didn't need money or financial institutions to build their empire, because they had a practically unlimited pool of labour to draw from. In return, they provided the populace with religious ceremonies and monuments, festivals, a variety of goods from extensive trade networks, and above all: stability. I hope this brief overview answered your question well enough. Feel free to ask any follow up questions. As for a source, check out the amazing book The Complete Illustrated History of the Inca Empire by Dr. David M. Jones :)