107 What has already happened and is still happening, was presented, as it were, in a vision before Our eyes when, while still some hope was left, We left nothing undone in the form suggested to us by Our Apostolic office and by the means at Our disposal, to prevent recourse to arms and to keep open the way to an understanding honorable to both parties. Convinced that the use of force on one side would be answered by recourse to arms on the other, We considered it a duty inseparable from Our Apostolic office and of Christian Charity to try every means to spare mankind and Christianity the horrors of a world conflagration, even at the risk of having Our intentions and Our aims misunderstood. Our advice, if heard with respect, was not however followed and while Our pastoral heart looks on with sorrow and foreboding, the Image of the Good Shepherd comes up before Our gaze, and it seems as though We ought to repeat to the world in His name: "If thou . . . hadst known . . . the things that are to thy peace; but now they are hidden from thy eyes" ( Saint Luke xix. 42).
Source: Summi Pontificatus (Vatican.va)