Who were the people that influenced the outcome of the civil war?

Lincoln - for appointing Grant as General-in-Chief.

Grant - for ending the system of prisoner-exchange, so the Confederates were certain to run out of manpower.

Sheridan and Sherman - for destroying farms and railroads, helping to starve the Confederate troops in the field.

Lee - for surrendering in orderly fashion, and not allowing some of his subordinates to take to the hills and conduct guerrilla warfare.