Treaty providing for the renunciation of war as an instrument of national policy
More commonly known as the Kellogg-Briand Pact, the Treaty providing for the renunciation of the renunciation of war as an instrument of national policy was initially adopted on August 27, 1928 by Germany, the United States of America, France, Great Britain, India, Japan, Poland, and Czechoslovakia. It went into force on July 24, 1929, at which time 32 more countries' instruments of definitive adherence brought them into the treaty; a number of other countries later ratified it. 
For its time, it was one of the most widely accepted international agreements. Depending on the starting date selected for the Second World War (e.g., the Manchuria Incident? Italian operations in Ethiopia? the invasion of Poland?), it was one of the most quickly ignored international agreements.
The key articles stated that the countries signing the treaty [condemned] "recourse to war for the solution of international controversies, and renounce it as an instrument of national policy in their relations with one another," and [agreed] that "the settlement or solution of all disputes or conflicts of whatever nature or of whatever origin they may be, which may arise among them, shall never be sought except by pacific means."
Relation to later developments
The document was important to the League of Nations. In 1935, Frank Kellogg, former U.S. Secretary of State and key negotiator of the Pact, cited it (referring to it as the Pact of Paris) with respect to the Italian invasion of Ethiopia (then commonly called Abyssinia). 
Its ideals certainly influenced the United Nations Charter, but are not as explicit in that document. An explicit renunciation of war does appear in the post-WWII Japanese constitution, and the revised German constitution, while not as strong in its phrasing, also speaks against military action.
It was considered a basis for the indictments for the charges of conspiracy against peace and waging aggressive war at the International Military Tribunal (Nuremberg) and the International Military Tribunal (Tokyo).
- Kellogg-Briand Pact 1928, Avalon Project, Yale University
- The Pact of Paris and the Relationship of the United States to the World Community: An Address Delivered over the Columbia Broadcasting System, The Avalon Project, Yale University, October 30, 1935