Despite overwhelming resources -- manpower, industrial might, and a powerful agricultural base -- the Union struggled during the first years of the conflict. The mere possession of these assets by no means ensured a Union victory. Not until its political and military leaders learned to harness that power and focus it on the enemy's source of strength, what Clausewitz called the center of gravity, did the war shift decisively in the Union's favor. Lincoln, Grant, Sherman, and Porter, all partners in command , did just that.