The opportunity arose for Robert E. Lee to reunite the United States of America at Gettysburg. In an egregious act of poor generalship, Lee sent fifteen thousand doomed men against an impossible, entrenched position. How do we know this to be the case? The amazing list of facts Lee was aware of at the time make it clear that Lee chose this time to try to sacrifice his army for the cause of reunion. While Lee had attempted to destroy the Confederacy many times prior to Gettysburg, the opposing generals were too inept to take advantage of the opportunities Lee presented. At Gettysburg, Lee finally found the situation he needed to create the win for the Federal army required to end the war. In fact, it appears Lee intended to have the whole of the Army of Northern Virginia destroyed, creating a much quicker end to the war than actually happened. Let's review a bit.
Lee has taken the Army of Northern Virginia into a Union State, Pennsylvania. This was not a long journey, Virginia and Pennsylvania are separated by only a few miles of Maryland at present and, in fact were border states in 1861 when Virginia seceeded from the Union. Lee had made this effort before, even arranging to have a complete set of his plans found by the Army of the Potomic (I wonder how many other sets were planted to be found). That effort resulted in the battle at Sharpsburg, Maryland (Antietam) and a subsequent tie rather than the defeat he had planned. The great battle of Antietam was interpreted by the North as a victory even though it wasn't simply because it was the first time Lee had been stopped, or seemed to have been stopped, from accomplishing his goals and the Federal army was not totally beaten. With the full plans of Lee in his hands, McClelland should have easily defeated Lee but was unable to because of the poor quality of the generalship involved. Further opportunities were given each general who succeeded McClelland and each in his turn failed to take advantage of the openings provided by Lee to be defeated by the Federal army. Ultimately Lee seemed to be the greatest general alive simply because his efforts to be defeated looked like daring genius. Astounding when you look at it.
So, what is the situation leading up to Gettysburg? Lee has recently fought a major battle against Hooker at Chanclersville, one he should have lost and tried desperately to lose. Lee has lost his right hand general, Jackson and has not appreciably damaged the Federal army. Hooker is still in charge of the Army of the Potomac and, while he has had his nose bloodied, is still the dangerous "fighting Joe" Hooker. Lee now abandons Richmond, uses J.E.B. Stuart to screen a move north, something that only lets Hooker know that Lee is moving north and Hooker follows, keeping on the inside of the circle, between Washington D.C. and the Army of Northern Virginia as is appropriate.
Now, things get interesting. As Lee enters Federal territory, Pennsylvania and Maryland, he allows his cavalry screen to wander off with orders to disrupt the supply areas of the Federal army, ostensibly causing the Federal army to move slowly and allowing Lee to resupply his army from the riches of south central Pennsylvania. With little cavalry, Lee will not know the situation of the Federal army and can be surprised, defeated piecemeal on Northern land, and the South will not rise again (so to speak). However, the Federal army now changes leaders and the impetuous "Fighting Joe" Hooker, the general Lee could count on to attack, attack, attack is no longer in charge. The more cautious but more competent general Meade is now in charge. Lee knows Meade will be more difficult to draw into a major battle than Hooker so Lee split up his army even more, discounts all cavalry reports on Federal army positons and continues with the separation of the Confederate army into resupply groups in south central Pennsylvania. Rapid movement at this time by Meade would totally defeat the Confederate army piece by piece. In spite of his bloodied nose, Hooker may have done exactly that. Meade, however is much more cautious and the Federal army is "screening" Washington D.C. for no good reason. The defenses of Washington D.C. are such that it is inpregnable to an army the size of Lee's Army of Northern Virginia. More than 400,000 troops are on hand nearly constantly around Washington D.C. with entrenched positions, an inside line of movement and reinforcement, abundant supplies and weapons. If these troops had been released to the field army, the Army of Northern Virginia would have been quickly overwhelmed by sheer numbers in spite of poor generalship.
So, Lee baited Meade to move quickly to smash the Confederate army. Lincoln urges Meade to do exactly that. Meade is in a tough spot. He has just taken over the Army of the Potomac and is well aware of the level of incompetent generalship available. He must have thought the Confederate army was larger and more concentrated than Lee was making available. Pinkerton seems to have kept their job as information specialists by exaggerating the enemy situation to frighten the generals into keeping them on a "just in case they're right" basis and it worked. The Union generals constantly got exaggerated reports of enemy size, weapons, and potential. This alone had created defeats in the past and surely slowed Meade at this point along with the reorganization Meade was required to do "on the fly" so to speak, as the army was following Lee.
At the same time Lee is baiting Meade to attack and win, Lee further separated his army, further ignores his advisors, and has the Army of Northern Virginia spread out over more than a hundred miles. He is on the outside of the supply line, has crossed a major river that could easily flood to impede passage, trapping him in the north, the Army of the Potomac could block passage to the south, trapping the Army of Northern Virginia to the death, he is in hostile territory, on less well known territory, and cannot be resupplied or reinforced from Richmond or any other southern area. Lee has deliberately walked into a trap and it only takes a small effort on the Union generalship to close the door on him. Was Lee trusting in the stupidity of northern generals to ignore the facts? Not likely. Lee was too aware of the potential the huge army the Federal had available to think he could just set this trap and not have it close. Incredibly, even at this level, the Federal leaders did not close the trap he so carefully set and he had to make an obvious error to "create" a defeat. Good grief!! Lee might as well have sent a written message to the newspapers saying "come and get me, I'm available" and all these signals were, and still are, ignored.
Now, knowing he is greatly outnumbered by the closing Federal army, Lee continues his separation of the Confederate army and will wait to be trapped. When this does not happen, he moves even further north along the Susquehanna river, creating a better trap. Just let the Federal army entrench south of Lee and remove the ability to return south. Then, close on the Confederate army and keep them in position, much as Grant did later starting with the Wilderness and ending at Appomatox Court House. Lee continues to wait. The ostensible argument for being in the north is that he will resupply his army with shoes and other consumer goods. Very few weapons are available for resupply here in south central Pennsylvania but there is food and shoes. Kind of a weak arguement isn't it. The other arguement was that he would draw Hooker (and later Meade) into a battle on Lee's choice of ground. Yet when the battle began, he threw this away and took what Meade and circumstances offered even when it was certain the Confederate position was not as strong as the Federal defensive position. Longstreet confronted Lee over and over on this and Lee changed the reason from finding a strong point to defeat the Federal army to the opinion that "they are there and I will attack them" as if that were a good reason. You have to remember, that the Federal army was "there" any time Lee wanted. He always knew where the Federal army was even though at Gettysburg, he could pretend he did not know. Stuart did not have all the cavalry with him and Lee had sufficient to know where the Federal army was and what it was doing. He pretended to have no confidence in the reports in order to continue with his plan of a defeat.
This time, Lee could not play the game of "lost plans" and was required to reach new levels of seeming arrogance and "ability" to create his defeat. Waiting patiently for the Federal army to close, Lee spread his army. When the clash finally came, Lee allowed the Federal army and circumstances to create the battlefield. Unfortunately for a lot of lives to be lost in the next year and a half, the Federal generals also allowed circumstances to create the battlefield. Even the most rudimentary evaluation of Lee's position shows the trap he has offered. Ultimately, he had to play a trump card of stupidity to create the win for the Federals he was working on.
Of course, it was important that Lee not appear to be actually causing a defeat. Once the battle began to be joined, he had to follow with what he had created. Cavalry off to the west someplace, disjointed units up the river and roving the countryside for forage, and a large, very large Federal army to the south, almost but not quite blocking a return to Virginia. Try playing that card for a win. Pretending Lee is a masterful tactician falls apart at this point. Pretending to go into Pennsylvania to gain a great win, destroy the Federal army, and occupy Washington or Baltimore disregards all reason and the facts of manpower and entrenched weaponry. Lee has set a trap alright, but it is for the Confederacy, not the Federal army. However, now Lee began to pull in the Army of Northern Virginia for the fight. A fight that should clearly have been the finish of Lee's army.
Once the armies are heavily engaged and positions solidified, Lee can see now that the Federal army is not going to take the bait and close the trap on the Army of Northern Virginia. Now, he creates disjointed attacks from first one side then another side, supposedly coordinated but actually handled in such a manner as to create nothing more than threats with much ammunition expenditure and loss of units available for fighting. As Lee gradually weakens the Confederate forces, he is faced with the problem of a major section of the Army of Northern Virginia that is fully intact, fully armed, and relatively unbloodied. A dangerous core of the Confederate army that he cannot keep available or the Federals will not be able to finish the job of destroying the Army of Northern Virginia. In order to destroy this solid core of his army, Lee came up with a plan that even the lowliest privates knew could not succeed. Lee took this flower of the Confederate army, 15,000 strong and sent them across one mile of open field and fences, uphill, directly in the face of the center of the Federal army which was well entrenched behind stone fences, had short interior lines of reinforcement, and were fully ready for the attack. Even a first year student at West Point would understand in advance the results of such an endeavor. When all else failed to get the Federals to destroy his army, Lee choose to destroy the Confederate army himself.
Now, trapped against a swollen river, out of ammunition for the big guns, deeply wounded and weakened, Lee is finally in the trap he has arranged. Lee now leaves the field slowly, taking his time, waiting at the Potomac until it can safely be crossed, not putting his army in battle array, simply stringing them our for destruction. A strong move by the Federal army will end the Army of Northern Virginia. Not without a fight, of course, but an end it will be. Casually, Lee waited for the final blow, arranging for it to be as painless as possible, given the circumstances of battles as bloody as they were then. Lee virtually offered the neck of his army to the sword. Meade, however, sat in place and allowed Lee to go back to Virginia. The next opponent Lee will face is Grant, a general of a different stripe. Grant would never have allowed Lee back to Virginia. Possibly even Hooker would have followed up and had blocked the way south. But Grant! Allow Lee to walk back slowly to Virginia? Not likely.
Nonetheless, Lee got his "high water mark" and the defeat needed to end the Confederacy. And it was close. The north was ready for one more loss to allow the south to go their way. There was a lot of sympathy with ending the war for a great many reasons. The south was a poor agrarian society, riddled with slavery (and the majority of the northern population cared not a whit for the plight of the slaves or blacks at all), the north was now experiencing great abundance, increased trade with the world, even increased trade with the Confederate States. There were many more reasons to let the southern states go their way and, after so much bloodshed, difficult to see that it was worth the continuation of such misery for such small stakes. However, Lee provided the impetus to bring on the end of the war and the reunion of the states. Gotta give him credit as the father of the rebirth of the Union.