Ultimately, Grant may be remembered as one of America's best generals. He is still the only general in history to capture three separate armies, and he presided over Lee's surrender at Appomattox in April 1865. He was also a fair man who treated the Confederates well during their surrender. He was simply determined not to allow the South to be victorious. He sometimes misjudged his generals, and perhaps left some in power longer than they should have been, but ultimately he led the Army to victory, and was responsible for the final battles that laid waste to the Confederacy and led to the end of the war.

He was also a technical general, who understood the need for supplies as much as the need for victory on the battlefield. He knew the South's army was undersupplied and desperate for provisions, and so, when a general was victorious, he ordered them to burn any supplies of value to create more hardships for the Confederates. It seems cruel, but it helped bring the South to its knees and ultimately end the war. Grant was not solely responsible for the end of the war, but his leadership helped make the end possible....

He was a fine general whose command earned respect from the fighting men, and that transferred to their attitude on the battlefield. Men who respect their commander will fight harder and longer because they feel his decisions are sound and his reasoning is just.
Some believe Grant made errors that helped prolong the war, but since he never let up on his determined attacks against Lee's army, these mistakes were overcome by his persistence and ultimate victory. Grant was not a perfect general or man, but he led the troops to victory when it mattered, and much of the North's final success is owed to his leadership, cunning, and knowledge. He influenced the war by his tenacity, which led to victory.

Reference

McPhearson, J.M. (2001). Ordeal by fire: The Civil War and reconstruction. New York: McGraw Hill.