Joseph Conrad 
Heart of Darkness 

This book was most famously adapted by Francis Ford Coppola in Apocalypse Now. Although that film moved the location to Vietnam, the novel is about Charles Marlow's life as an ivory transporter down the Congo River in Central Africa. It delves into the way people decide what constitutes a barbarian society and what constitutes a civilised society. It also explores attitudes on colonialism and racism that were part and parcel of European imperialism.