Kellog-Briand Pact
In 1928 Aristide Briand and Frank. B. Kellogg signed the Kellogg-Briand Pact (Pact of Paris). The treaty outlawed war between France and the United States. The US Senate ratified it in 1929 and over the next few years forty-six nations signed a similar agreement committing themselves to peace.
Primary Sources
(1) Aristide Briand, speech (7th September, 1929)
Among peoples who are geographically grouped together like the peoples of Europe there must exist a sort of federal link. It is this link which I wish to endeavour to establish. Evidently the association will act mainly in the economic sphere. That is the most pressing question. But I am sure also that from a political point of view, and from a social point of view the federal link, without infringing the sovereignty of any of the nations which might take part in such as association, could be beneficial.