Grant’s masterpiece was the Vicksburg campaign. It really is vastly underestimated in the historiography.
Lee’s critical mistake was going north to Gettysburg instead of standing on the defensive in Virginia and sending Longstreet West to help Johnson stop Grant. By July 4th 1863 the war was lost for the Confederacy.
I agree about Vicksburg. In conception Grant basically stood alone. Even Sherman didn’t think it would work. But it did.
Examining a map of the nation, Lincoln made a wide sweeping gesture with his hand then placed his finger on the map and said, “See what a lot of land these fellows hold, of which Vicksburg is the key. The war can never be brought to a close until that key is in our pocket.” It was the president’s contention that, “We can take all the northern ports of the Confederacy, and they can defy us from Vicksburg. It means hog and hominy without limit, fresh troops from all the states of the far South, and a cotton country where they can raise the staple without interference.” Lincoln assured his listeners that, “I am acquainted with that region and know what I am talking about, and, as valuable as New Orleans will be to us, Vicksburg will be more so.”
Upon receipt of Grant’s message, Lincoln sighed, “Thank God,” and declared “The Father of Waters again goes unvexed to the sea.”
Lee went north in 1863 in no small part to prevent his army from being split and part sent west in a futile effort to save Vicksburg.