General-in-Chief Winfield Scott, a veteran of the 1812 and Mexican wars, devised a three-part-strategy for winning a long war: use the U.S. Navy to blockade Southern ports, cutting off essential supplies from reaching the Confederacy, take control of the Mississippi River, dividing the Confederacy in two, and raise and train an army 500,000 strong to conquer Richmond.
The first two parts of the strategy proved easier to achieve than the third, but ultimately all three were important in achieving Northern victory.