One reason why most European counties started imperializing Africa was for there raw materials like coal and metal. As Europe industrialized and modernized the need for more materia increased. The new inventions from the industrialization like stream boats allowed countries to get there.
Britain was doing trading with china, they imported opium. Many Chinese people became addicted and the problem of it rose. As a result China had thrown out a shipment of the drug.Britian retaliated and fought China.