McClellan was like Montgomery before Alamein: he wasn't going to move an inch unless he had overwhelming superiority in men, weapons, and supplies. When he was finally forced to move (he invaded the James Pennisula) he bungled the attack so badly that he was nearly pushed into the water.

One of the big strategic problems in the ACW was that generals were still tied to notion that every single strong point had to be defeated. For example, Kennesaw Mountain could have been surrounded and forced into surrender by lack of supplies but Sherman had been schooled that it had to be reduced, that it posed a threat to his rear, and so forced his men to attack up a very steep slope.

Moreover, the weapons available had far outstripped the thinking and tactics of the military minds of the time. Fredricksburg is one example of it, Shiloh and Gettysburg are others.