Hong Kong imported raw materials from China and other countries and exported products to China and overseas markets. Local industries were therefore sensitive to the changing situations of these regions. The external factors that affected Hong Kong industries prominently were the political and economic conditions in China, Japanese invasion in China, the disruption of trades during the World War I and the economic depression worldwide. The trade policies in Europe that aimed to protect their local industries also affected Hong Kong industries in significant ways, the most influential one being the Imperial Preference system.