Blight's review, combined with the recent History Channel treatment convinces me that Grant's first motivation in resuming his military career at the outset of the Civil War was to restore his reputation, which would give him better job prospects in Illinois after the war was over. The conflict was expected to be brief, and by the time he had a Brig Gen'ship of volunteers, he had probably accomplished much of what he intended. I don't think he ever wanted to go east and fight in Virginia.
I think both Chernow and Blight miss how dominant debt and tax issues became between 1865 and 1868. Taxes remained high. There was a surplus as the economy grew, and the ratio of federal debt/GNP improved. The British were heavily invested in US railroads and cities and more British investment was desperately needed. Cotton production had to restored, as part of dealing with the ruin of the south. The Union Pacific part of the continental railroad was most likely known to be an engineering success and a financial fraud. Someone was going to have bail the Union Pacific out of insolvency, and Jay Gould was one of the few capable of raising the money.