In the late 19th century, King Leopold II of Belgium privately controlled a large area in Africa that would be known as the Congo Free State. His reign in Congo earned infamy due to his mistreatment of the local peoples. He extracted ivory, rubber, and minerals in the upper Congo basin for sale, even though his original purpose was to uplift the people and develop the area.
Ten million people lost their lives under his rule, and the forced labor system killed 20% of the population. There were many books that exposed the atrocities, such as: Joseph Conrad's Heart of Darkness, and Arthur Conan Doyle's The Crime of the Congo. In 1908, due to public pressure and diplomatic maneuvers led to the end of Leopold II's rule, and led to the annexation of Congo as a colony of Belgium, now called the Belgian Congo.
For the next fifty years, the government and private enterprise worked closely together, not helping the indigenous population. They also had a large degree of racial segregation, with the post-WWII white immigrants being treated much higher than the native population.
In 1960, as a result of their recent pro-independence movement, they finally gained independence from the Belgians, however they were largely unprepared, and for the next five years, a bitter conflict occurred in the Congo, called the Congo Crisis.
In July of that year, the mineral rich province of Katanga declared itself independent from Congo. The mining province of South Kasai also seceded from the country. Interestingly enough, the Belgian government offered military support to those provinces, but on July 14th, the UN adopted Resolution 143, calling for total Belgian withdrawal from the Congo and their replacement with a UN-commanded force. Soviet intervention led to the creation of a new government, and they were soon expelled by Mobutu, the head of the army.
Later, with the support of UN troops, Leopoldville (Congo) defeated Katanga and South Kasai in early 1963. Afterward, east militants called "Simbas" rose up in East Congo. They took control of a significant territory, and slowly, but surely Leopoldville retook the territory, and the Congo established an independent, unitary state under Mobutu.
(I'll post a part 2 later, with the Congo wars, and the rest of Congo history (1965- now))