The move that won the battle of Gettysburg...

When Fed & CSA forces first encountered each other at Gettysburg, neither side knew how close their two armies were to each other. However, soon as the CSAs realized they were facing regulars, not Penn. militia, they sent word to their commander, Gen. Heth, who sent several more units to the scene at once.

The Feds didn't have nearly as many men in that immediate area, & quickly realized it. Gen. O. O. Howard told his men to fight, but be prepared for retrograde advance before they could be overwhelmed by greater numbers. He sent several units to Cemetery Ridge, outside of town, & told them to dig in as best they could; it looked like a good defensive position.

Meanwhile, more CSAs arrived, & the Feds were forced to retreat or be overrun, & they did, to Cemetery Ridge. Soon, the Feds had a strong defensive position there.

Howard's move to quickly occupy that ridge & made a strong defensive line there was the move that proved to be the winner of the battle, as 2 days later, Lee's attempt to storm it with Pickett's(Actually Longstreet's) Charge" was crushed, & the Rebs no longer had enough men for any meaningful attack on the Fed defensive line.

(A little PS: While Lincoln at first roundly criticized Meade for failing to attack Lee's retreating army, that army was weakened, but still in good order, & Lee had them prepared for a new attack . Meade's own forces had also suffered heavy losses, & was not in its best shape. There was certainly no guarantee Meade's army would've defeated Lee's army had they clashed again. Meade knew that, & didn't want to risk suffering a humiliating defeat that woulda thrown away his recent victory.)

 

Lee's aim in invading Pa. was threefold: First, to try to take pressure off Vicksburg by causing Grant to sens at least part of his army there. Second, to take the fighting out of Virginia to enable its people to have a good crop harvest, and third, to win victories to make the Northerners, who were war-weary, to seek peace & recognize the CSA as a separate nation.

Lee didn't want to fight at Gettysburg, but, once a substantial part of his army was engaged due to accidental encounters by both sides, he resolved to a full-scale battle. But he was infected by "victory disease" because of his resounding recent victories at Fredericksburg & Chancellorsville. He convinced himself that his army could whip the Army of the Potomac any time, anywhere.

Lee had known the tendencies of Burnside & Hooker when each commanded the AOP. However, he didn't know much about Meade, except that Meade wouldn't blunder as his forebears had done.

 

Two theories for the Rebel loss at Gettysburg should be dispensed with as false.

The first is that Gen. Ewell, appointed to take Stonewall Jackson's place after the latter died, could've taken Cemetery Ridge on the 1st day of battle. Lee told him to take it "if practicable". However, Ewell's men were tired after a long march & hard fight, & he saw the feds had made a strong position there, with reinforcements not far away. Also, Lee wouldn't send Gen. A. P. Hill's corps to help him, so Ewell chose not to attack, & his subordinate, the normally-aggressive Jubal Early, agreed with him.

Besides, there's no guarantee Ewell's corps would've captured that hill, even with well-rested men, as the Feds had indeed made a strong, well-fortified position there, including artillery. But Ewell did attack the next day, but in vain. However, he & his men performed well until the battle of Spotsylvania, where Ewell made several blunders that cost many casualties & almost lost the battle.

The other theory was that Gen. Longstreet failed to attack the Fed left flank early on July 2 as Lee had ordered, as Longstreet didn't like that plan at all. However, Longstreet acted swiftly as he could. His corps was simply not in position for an early attack, & Longstreet tried to form it up quickly as possible. However, it was not in position to attack until afternoon, and, while having some success, especially due to Fed. Gen. Sickles' blunder, his attack was stopped, as the Feds were able to reinforce their positions. AGAIN, THIS WAS NOT LONGSTREET'S FAULT, & Lee later said so himself.

And, while Longstreet was very-much-against Lee's assault on the Fed center on July 3, he carried out his orders as best he could, in an attack which brought about "Pickett's charge" & a great many Rebel casualties.

Later, Longstreet became reviled in some Southern circles because he crtitcized Gen. Lee, who by then had died & couldn't defend himself. Much of the criticism was because of several speeches by Jubal Early, the originator of the "Lost Cause" movement, which almost-worshipped Lee & blamed Longstreet for the loss at Gettysburg. This theory was still alive in the South long after Early & Longstreet had both died.

 

Actually, Lee said, "if practicable". The Feds were half-expecting an attack when they saw Ewell's corps arrive. Now, while Stonewall woulda almost-certainly attacked, victory was by no means assured. The Rebs woulda been just-as-tired had they been under Jackson, & more and more Feds were arriving every moment. They'd hurriedly madea decent defensive line, that they'd been working on ever since Gen. Howard's men first arrived, which, by the next day, was practically impregnable.

Thus, Jackson's corps might well have been spent & unable to participate in next days' battle. Lee wasn't fully aware of the Fed troop disposition when Ewell arrived, so that's why he said "if practicable", leaving it to Ewell's discretion once Ewell had surveyed the Fed defenses. True, Eewll was no Jackson, but his men were Jackson's old corps & could certainly still fight hard.

Lee was infected with "victory disease", having twice whupped that same Fed army severely, recently. Thus, he didn't heed Longstreet's advice to try to maneuver the feds outta the strone defensive position they'd taken. Longstreet & Lee both knew Meade was a better general than the recent Army of the Potomac commanders, Burnside & Hooker. And they knew Meade was an able defensive commander. But Lee had convinced himself that his army could beat this Fed army anywhere, no matter who was commanding it.

BTW, Gen. Custer, while not doing so hot at Little Bighorn a few years later, was a true hero near Gettysburg, on the 3rd day of that battle. He caught Stuart's cavalry, numbering some 4000, in a fairly-narrow passage thru some woods, & attacked it head-on with some 500 Michigan Wolverines cavalry. His attack stalled the Rebs, causing some confusion among them, as the attack was a surprise. Custer & his men escaped lest they be overwhelmed if Stuart had found another nearby way thru the woods, but, due to the confusion caused by Custer's attack, Stuart wasn't sure of the size of the Fed cavalry, & his corps had become disorganized, so he called off his part of Lee's plan, which was for him to attack the rear of the center of the fed line in conjunction with "Pickett's Charge". Had Stuart succeeded, the Rebs could well have won the battle.