It all began in the late 1880's when the Peruvian, Julio Cesar Arana, started a rubber-collecting business known as Casa Arana -- later called the Peruvian Amazon Company. The company, with its main office in Iquitos, made him a multi-millionaire at the expense of the Indigenous population. (Think King Leopold and the Congo).
In order to collect rubber, Arana used the natives as virtual slaves. They were taken from their land and forced to work in deplorable conditions and forced to pay more than they made for the little food that they were given. Thus, they were always in debt to the company. If they produced too little, they were tortured. If they tried to escape, they were killed. Rape, torture, disease, and murder were commonplace. During the almost 40 years that the company existed, the native population in the area went from 50,000 to 10,000 -- 80% of the natives of the region had disappeared.
The Amazon Journal of Roger Casement