A number of Historians have attempted, over the years, to define the Civil War partnership of U.S. Grant and William Tecumseh Sherman; and identify "what it was that made that partnership successful." General Oliver O. Howard, USMA Class of 1854, came to know the two leaders after he was transferred to the West following his participation at Gettysburg; he first made their acquaintance during the Campaign for Chattanooga in October 1863. This is General Howard's observation:
References: http://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/America/United_States/Army/USMA/Cullums_Register/1634*.html General O.O. Howard bio
https://archive.org/details/autobiographyofo01inhowa/page/n7 Autobiography of General Oliver O. Howard (pages 474 - 475).