Before beginning this, and this is the last Civil War entry for today, I will repeat again the challenges the Union had to face: it had to conquer and occupy a territory the size of European Russia, with extremely primitive infrastructure, chock-full of guerrillas, waging an ideological war and against an enemy who had merely to stalemate them. As will be recounted in the series on the World Wars, two German armies with a much better position than the Union, even, relative two equally primitive (at the start) Russian Empires failed in this exact same task, but the Union not only succeeded but did so that the Bitterenders aside there was no permanent War without Pity, War without End. It did take four years, but then again as noted this was tried twice in the 20th Century with failures in both instances.
The first obvious explanation is in fact obvious, in Ulysses S. Grant and William T. Sherman, under Abraham Lincoln the Union had a more talented political leadership and pair of ultra-competent generals against a Confederacy with one over-aggressive general who won Pyrrhic victories and one truly visionary cavalry general. Lincoln endured drama llamas with his generals that Davis was congenitally incapable of doing so with his. One Confederate general behaving as was the wont of Generals McClellan and Hooker and that general would have been cashiered for the duration of the war. Where Union generals won victories, like Rosecrans in the Tullahoma Campaign, or Grant in the Donelson, Pittsburg Landing, Vicksburg, and Overland Campaigns it was in pursuit of an objective beyond an individual battle. It was also done with desire to avoid an excess of casualties or big, bloody battles. Certainly the Union's incompetent leaders were such due to not taking risks
where the Confederacy's "best" general, Lee, repeatedly took more casualties than an enemy that began in 1861 with 4:1 manpower superiority.
To me another major reason that the Union won as opposed to the Confederacy was that leaders like Grant pursued a consistent strategy designed to not merely go after territory or psychology, but the enemy army with resources to make that effective.
General Lee had the same overall vision, however his resources were dramatically unequal to the task and he took much higher casualties than his enemy for no overall gain that made them worthwhile. Grant was the same kind of general, but was much more careful about his resources. His major mistake at Pittsburg Landing was not considering the possibility the other side would hit him first, his major frontal assault at Cold Harbor was his one and only incident like that in the duration of the war and it was his one and only incident like that in the duration of the war.
Bobby Lee did that six times during the Seven Days and was still launching those assaults into the Battle of Five Forks, and unfortunately for the Confederacy Longstreet and Jackson were the subordinate officers to a bloodthirsty sumbitch who sacrificed lives for bupkiss.
Another big reason to me as to why the Union succeeded in a task Germany tried twice and failed both times at is that the Union leadership was amply able both to exploit the mistakes of the other side (and in real war battles are won by the side that screws up less severely and less often) while its own mistakes were seldom, if ever correspondingly exploited. In fact due to Grant's curbstomping Lee in the Overland Campaign and Grant's unbroken string of victories from Donelson to Chattanooga it can be said that the Union also benefited from a real-life Mary Tzu who won damned near every battle for the Union that counted until 1864, when his good friend Sherman and Thomas picked up the slack.
Ordinarily I'd scoff at a book that has a single general who'd do something like that, but then there's Grant in the Civil War in real life saying "that the only difference between reality and fiction is reality must be believable." So what ultimately was the reason the Confederacy failed to defend a region the size of European Russia *despite* ample use of irregular warfare and having multiple entire armies wielded against an enemy that had to conquer, as opposed to stalemate? Three simple words: Hiram Ulysses Grant.
They were given the H.U.G. of doom.
To illustrate these points: at Henry and Donelson, Grant seized the Initiative and at a cost of 2,832 men of 24,531 captured 17,000 Confederates. At Vicksburg, with parity with two Confederate armies (50,000 against 50,000) in the actual campaign Grant lost 9,362 compared to the Confederate 40,178) and even managed to make a siege less costly to him, the attacker, than Pemberton, the defender. At Chattanooga with an army group whose main subgroup was starving and in a bad lot he inflicted in a headlong attack (which almost always failed) 6,667 Confederate casualties to 5,814.
The Overland Campaign took 50,000 casualties in two months to drive Lee into Petersburg, where he remained for the rest of the war and saw the first stirrings of later WWI tactics.
Now, Lee's magnum opes with the Seven Days' (built his reputation as Donelson did Grant's) were 20,000 to the Union's 16,000. At Chancellorsville with 60,000 men he lost 12,674 men while Hooker's army of 120,000 lost 17, 287. Essentially Lee even in his best battle of them all lost 19% of his men compared to Hooker's lower totals. His Overland Campaign attrition strategy designed to *avoid* the Petersburg Siege outcome and its when, not if, ending was a complete strategic failure as Grant consistently outmaneuvered Lee and forced him steadily south and back, as opposed to Lee's having chance to intimidate Grant. Overall, Grant the "butcher" had 154,000 casualties from a Northern manpower pool of 3,000,000 and a Southern addition of 500,000. Where Lee, from a total manpower pool (lessened to 800,000 due to the 200,000 Southern whites in Grant's 3,500,000 total) took 201,000 casualties.
Now, *this* is why Grant should properly be seen as someone who would be unrealistic in any reality but this one.