The Overland and Petersburg campaign occurred inside of three other important factors. The first is Grant's mind- his mental abilities and skill at using them to frame the war and figure out how to prosecute it. Since Grant didn't spring fully formed from the mind of Zeus, your probably going to need to show either an early use of his mastery, or its evolution over time as he learned and refined. Some references to how X mimicked Vicksburg, or differed significantly in concept etc.
Secondly, since Grant was not a field commander but occupied a role more like Ike in WWII in many ways, your going to need to reference his planning with Sherman and other Union commanders to created a system where the Confederacy was never able free up and shift reserves and achieve and then sustain even a local reversal of the Union tide.
Finally, a reference to Scott's Anaconda plan and how or if this vision shaped the way he framed the prosecution of the war. Combined Operations of the Civil War by Reed and Milligan argue that Plan was ineffectual since the Union was not able to brign its commanders to hell. Grant did bring them to heel and then did conduct an organized campaign to reduce the South.