When the second World War came to an end in 1945, it was not possible for the mandatory power to give full effect to the policy set out in the White Paper of 1939. The League of Nations, to which that document was to have been submitted for approval, no longer existed. And the tragic fate of the Jewish people in Europe had created a demand that the Palestine problem should be examined again in relation to the needs of the survivors of racial persecution.
This demand was strong in the United States. In August, 1945, President Truman wrote to Mr. Attlee (e.g. Prime Minister of Great Britain) suggesting that the concession of 100,000 immigration certificates for Palestine would be an important contribution to the settlement of displaced European Jews.
Source: The Political History of Palestine under British Administration Published (by His Britannic Majesty’s Government presented in July, 1947, to the United nations Special Committee on Palestine) Published at Jerusalem 1947 (pg 46)