The United Nations Charter states that treaties must be registered with the UN to be invoked before it or enforced in its judiciary organ, the International Court of Justice. This was done to prevent the proliferation of secret treaties that occurred in the 19th and 20th century. Section 103 of the Charter also states that its members' obligations under it outweigh any competing obligations under other treaties.
In which centuries did a proliferation of secret treaties occur that led the United Nations Charter to include an obligation to register treaties to be invoked before it?
19th and 20th century