IIRC U.S. Grant played a significant role at Shiloh in April 1862, helping to rally the Union forces and stem the Confederate attacks. The fighting was so fierce that the Southern commander, Albert Sidney Johnston, was killed, and had to be replaced by IIRC P.G.T Beauregard. WI Grant had ended up being killed during Shiloh as well ? How would the course of the ACW have proceeded without him, esp without his 1864-65 attritional strategy which finally defeated Lee ? Who could his likely successors have been, and how would they have fared in his place ?