Complex sentence: In 1878, King Léopold II of Belgium, who had previously founded the International African Society in 1876 invited Stanley to join him in researching and'civilizing' the continent.
Split into simpler sentences: In 1878, King Léopold II of Belgium, who had previously founded the International African Society in 1876, invited Stanley to join him. The International African Society had the goal of researching and'civilizing' the continent.