Chief, here is one of those letters,

"You and I both anticipated that the cause of the country would be advanced by making the attempt to provision Fort Sumter, even if it should fail, and it is no small consolation now to feel that our anticipation is justified by the result." ~ Lincoln to Gustavus Fox, in a letter dated May 1 1865. The phrase 'even if it should fail' is a tip off to Lincoln's real motivations.

Google will point you to many references to this letter