My dear Mr. President:
The Republic of Portugal and the United States of America have long enjoyed the full and complete friendship of each other. Because of this great friendship, and our mutual desire to insure its continuation, I desire to relate to you the urgent reasons that have compelled me to dispatch to the assistance of the friendly French possessions in North Africa a strong Army of the United States.
I have been advised by very reliable sources of information that in the near future it is the intention of Germany and Italy to occupy the French North African colonies with a large military force.
I know that it will be quite clear to you that prompt and effective action should be taken to deter such an attempt by the Axis Nations, with its inherent danger to the defenses of the Western Hemisphere.
To forestall occupation by the Axis Nations of the French North African possessions and protectorates, and thus to insure the defense of American Nations, is the only reason which prompts the dispatch of powerful United States forces to the area. It is hoped that French North Africa will not suffer in any way from the destruction of war on its own soil.
I desire to reassure you fully that the presence of American military forces in French North Africa presages in no manner whatsoever, a move against the people or Government of Portugal or against any of Portugal's continental or island possessions. Since I realize that Portugal really desires above all else to avoid the horrors and devastation of war, I hope that you will accept my solemn assurance that your country should have no fear of the motives of the United Nations.
I am, my dear Mr. President,
Your sincere friend,
Franklin D. Roosevelt, Letter to the President of Portugal on America's Intentions in North Africa. Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/210144