Leopoldo II never conquered the Congo, and never inherited it. He persuaded the world to gift it to him.
Playing the humanitarian (funding anti-slavery NGOs, hosting an Anti-Slavery Conference in a masterpiece of hypocrisy), he got fourteen nations at Berlin in 1885 to hand him a territory of 20 million people. As personal property.
What followed was rubber and ivory extracted through slavery, hostage-taking and severed hands used as currency. The population halved, to 10 million.
The exposure came from a shipping clerk (Edmund Morel) and a British consul (Roger Casement, report of 1904), two of history’s great whistleblowers.
Belgium only took the Congo from him at his death.