<P> As a theory, the United States' 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). </P> <P> 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 . </P> <P> The Open Door Policy was a principle, never formally adopted via treaty or international law . It was invoked or alluded to but never enforced as such . Starting with the 1931 Japanese seizure of Manchuria and the creation of Manchukuo, however, the policy was broken with impunity and with increasing frequency . </P> <P> Technically, the term Open Door Policy was only applicable before the founding of the People's Republic of China in 1949 . After Deng Xiaoping took office in 1978, the term referred to China's policy of opening up to foreign business that wanted to invest in the country, setting into motion the economic transformation of modern China . </P>

When did china have a closed door policy