Message to the President of Poland on Bombing of Civilians.
I have received your telegram stating that as the result of the bombing by German aircraft of Polish towns and villages possessing no considerable military objective thousands of the civil population of Poland are dead or wounded.
It had been my hope following the receipt from the several belligerent powers of the replies to my appeal of September 1, in which they stated their intentions to limit the operations of their air forces to military objectives, that the world would be spared the horror of witnessing during this war the bombing of open towns and villages and the slaughtering of thousands of innocent and defenceless men, women, and children.
I have been deeply shocked, therefore, by the statements contained in your telegram as well as by reports received from other sources, including officials of this Government in Poland at the scene of hostilities.
In view of the hundreds of thousands of lives which may be at stake, it is my earnest hope that the Governments of the belligerent countries will renew their orders prohibiting the practice of bombing civilians in unfortified centers of population from the air, and that they will take measures to assure themselves that their respective air forces are showing that regard for the lives of non-combatants which their replies to my appeal of September I have led the world to expect.
Franklin D. Roosevelt, Message to the President of Poland on Bombing of Civilians. Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/210058