His Excellency
Adolf Hitler,
Chancellor of the German Reich,
Berlin, Germany
In the message which I sent to you on April 14 last I stated that it appeared to me that the leaders of great nations had it in their power to liberate their peoples from the disaster that impended, but that unless the effort were immediately made with good will on all sides to find a peaceful and constructive solution of existing controversies, the crisis which the world was confronting must end in catastrophe. Today that catastrophe appears to be very near at hand indeed.
To the message which I sent to you last April I have received no reply, but because of my confident belief that the cause of world peace—which is the cause of humanity itself—rises above all other considerations, I am again addressing myself to you with the hope that the war which impends and the consequent disaster to all peoples everywhere may yet be averted.
I therefore urge with all earnestness—and I am likewise urging the President of the Republic of Poland--that the Governments of Germany and of Poland agree by common accord to refrain from any positive act of hostility for a reasonable and stipulated period, and that they agree likewise by common accord to solve the controversies which have arisen between them by one of the three following methods: first, by direct negotiation; second, by submission of these controversies to an impartial arbitration in which they can both have confidence; or, third, that they agree to the solution of these controversies through the procedure of conciliation, selecting as conciliator or moderator a national of one of the traditionally neutral states of Europe, or a national of one of the American republics which are all of them free from any connection with or participation in European political affairs.
Both Poland and Germany being sovereign Governments, it is understood, of course, that upon resort to any one of the alternatives I suggest, each nation will agree to accord complete respect to the independence and territorial integrity of the other.
The people of the United States are as one in their opposition to policies of military conquest and domination. They are as one in rejecting the thesis that any ruler, or any people, possess the right to achieve their ends or objectives through the taking of action which will plunge countless millions of people into war and which will bring distress and suffering to every nation of the world, belligerent and neutral, when such ends and objectives, so far as they are just and reasonable, can be satisfied through processes of peaceful negotiation or by resort to judicial arbitration.
I appeal to you in the name of the people of the United States, and I believe in the name of peace-loving men and women everywhere, to agree to the solution of the controversies existing between your Government and that of Poland through the adoption of one of the alternative methods I have proposed. I need hardly reiterate that should the Governments of Germany and of Poland be willing to solve their differences in the peaceful manner suggested, the Government of the United States still stands prepared to contribute its share to the solution of the problems which are endangering world peace in the form set forth in my message of April 14.
Franklin D. Roosevelt, Message to Adolf Hitler on the Poland Crisis Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/209874