The theory of the Open Door Policy originated with British commercial practice, as reflected in treaties concluded with the Qing dynasty China after the First Opium War (1839–42). The Open Door concept was first seen at the Berlin Conference of 1885, which declared that no power could levy preferential duties in the Congo. As a concept and policy, the Open Door Policy was a principle that was never formally adopted via treaty or international law. It was invoked or alluded to but never enforced as such. The policy collapsed in 1931 when the Japanese seized and kept Manchuria, despite international disapproval. Technically, the term Open Door Policy is applicable only before the founding of the People's Republic of China in 1949. After Deng Xiaoping took power in 1978, the term referred to China's policy of opening up to foreign business that wanted to invest in the country, which set into motion the economic transformation of modern China.