An "Open Door" policy provides far maintenance in a certain territory of equal commercial and industrial rights for the nationals of all countries. As a policy, it was first advanced by the United States, but it was in the typical most-favored-nation clause of the treaties concluded with China after the Opium War (1839-42). Although the Open Door is generally with China, it also received recognition at the Berlin Conference of 1885, which declared that no power could preferential duties in the Congo basin.