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Economy during Leopold's rule

While the war against African powers was ending, the quest for income was increasing, fuelled by the aire policy. By 1890, Leopold was facing considerable financial difficulty. District officials' salaries were reduced to a bare minimum, and made up with a commission payment based on the profit that their area returned to Leopold. After widespread criticism, this "primes system" was substituted for the allocation de retraite in which a large part of the payment was granted, at the end of the service, only to those territorial agents and magistrates whose conduct was judged "satisfactory" by their superiors. This meant in practice that nothing changed. Congolese communities in the Domaine Privé were not merely forbidden by law to sell items to anyone but the state; they were required to provide state officials with set quotas of rubber and ivory at a fixed, government-mandated price and to provide food to the local post.

In direct violation of his promises of free trade within the CFS under the terms of the Berlin Treaty, not only had the state become a commercial entity directly or indirectly trading within its dominion, but also, Leopold had been slowly monopolizing a considerable amount of the ivory and rubber trade by imposing export duties on the resources traded by other merchants within the CFS. In terms of infrastructure, Leopold's regime began construction of the railway that ran from the coast to the capital of Leopoldville (now Kinshasa). The railway, now known as the Matadi–Kinshasa Railway, was completed in 1898.

By the final decade of the 19th century, John Boyd Dunlop 's 1887 invention of inflatable, rubber bicycle tubes and the growing usage of the automobile dramatically increased global demand for rubber. To monopolize the resources of the entire Congo Free State, Leopold issued three decrees in 1891 and 1892 that reduced the native population to serfs. Collectively, these forced the natives to deliver all ivory and rubber, harvested or found, to state officers thus nearly completing Leopold's monopoly of the ivory and rubber trade. The rubber came from wild vines in the jungle, unlike the rubber from Brazil (Hevea brasiliensis), which was tapped from trees. To extract the rubber, instead of tapping the vines, the Congolese workers would slash them and lather their bodies with the rubber latex. When the latex hardened, it would be scraped off the skin in a painful manner, as it took off the worker's hair with it.

The Force Publique (FP), Leopold's private army, was used to enforce the rubber quotas. Early on, the FP was used primarily to campaign against the Arab slave trade in the Upper Congo, protect Leopold's economic interests, and suppress the frequent uprisings within the state. The Force Publique's officer corps included only white Europeans (Belgian regular soldiers and mercenaries from other countries). On arriving in the Congo, the army included men from Zanzibar, West Africa, and eventually from the Congo itself. In addition, Leopold had been actually encouraging the slave trade among Arabs in the Upper Congo in return for slaves to fill the ranks of the FP. During the 1890s, the FP's primary role was to exploit the natives as corvée labourers to promote the rubber trade.

Many of the black soldiers were from far-off peoples of the Upper Congo, while others had been kidnapped in raids on villages in their childhood and brought to Roman Catholic missions, where they received a military training in conditions close to slavery. Armed with modern weapons and the chicotte —a bull whip made of hippopotamus hide—the Force Publique routinely took and tortured hostages, slaughtered families of rebels, and flogged and raped Congolese people with a reign of terror and abuse that cost millions of lives. One refugee from these horrors described the process:

We were always in the forest to find the rubber vines, to go without food, and our women had to give up cultivating the fields and gardens. Then we starved... When we failed and our rubber was short, the soldiers came to our towns and killed us. Many were shot, some had their ears cut off; others were tied up with ropes round their necks and taken away.

They also burned recalcitrant villages, and above all, cut off the hands of Congolese natives, including children. The human hands were collected as trophies on the orders of their officers to show that bullets had not been wasted. Officers were concerned that their subordinates might waste their ammunition on hunting animals for sport, so they required soldiers to submit one hand for every bullet spent. These mutilations also served to further terrorize the Congolese into submission. This was all contrary to the promises of uplift made at the Berlin Conference which had recognized the Congo Free State.