Washington, D.C., was in a panic. 72,000 Confederate troops were just 60 miles away near Gettysburg, Pennsylvania.
After the Confederate victory at the battle of Chancellorsville, Robert E. Lee was under a time deadline. Mounting casualties of the war were causing Lincoln’s popularity to fall, so if Lee could get a quick victory at Gettysburg, he could pressure Lincoln to a truce.
But this window of opportunity was fast closing, as Union General Ulysses S. Grant was about to capture Vicksburg on the Mississippi, which would divide the Confederacy and free up thousands of Union troops to fight Lee in the east.
Unfortunately for Lee, his tremendously successful general, “Stonewall” Jackson, had died two months earlier, having been mistakenly shot by his own men. On the Union side, Lincoln replaced Maj. Gen. Joseph Hooker with Maj. Gen. George Meade to command the 94,000 men of the Union Army of the Potomac.
The Battle of Gettysburg began July 1, 1863. After two days of intense combat, with ammunition running low, General Robert E. Lee ordered a direct attack. Confederate General James Longstreet disagreed with Lee’s plan, resulting in his delayed advance till after all the Confederate artillery had been spent, leaving no cover fire.
Historians speculate that if General Longstreet had made a timely attack, the Confederates may have won the day.
[excerpted]http://www.wnd.com/2016/07/the-battle-that-changed-the-course-of-history/