1. Gettysburg ended the Confederacy’s last full-scale invasion of the North.

Following his victory at Chancellorsville, a confident Confederate General Robert E. Lee led his Army of Northern Virginia across the Potomac River into Union territory in June 1863. Lee had invaded the North the prior year only to be repelled at Antietam, but on this occasion his army was at the peak of its strength as it pressed across the Mason-Dixon line into Pennsylvania.

A victory at Gettysburg could have launched Confederate forces to Philadelphia, Baltimore or even Washington, DC. Instead, Lee’s army suddenly shifted from offense to defense after the defeat and 10 days later crossed back over the Potomac into Virginia. Never again would the Confederacy regain its momentum and push as deeply into Union territory, which is why many historians consider Gettysburg the “high water mark of the rebellion.”

2. The battle proved that the seemingly invincible Lee could be defeated.

While Lee had been fought to a draw at Antietam, the Union high command had yet to achieve a decisive victory over the Confederate general as the summer of 1863 began. In spite of being outnumbered, Lee had engineered significant victories at Second Bull Run, Fredericksburg and Chancellorsville among others. Meanwhile, Abraham Lincoln relieved a string of Union generals—George McClellan, Ambrose Burnside and Joseph Hooker—of command of the Army of the Potomac due to their failure to stop Lee’s army. Lincoln’s latest choice—General George Meade—had been installed just days before Gettysburg. Lee’s sterling record inspired complete trust in his troops and fear in his enemy. The Battle of Gettysburg, however, finally proved the bold general to be fallible.

3. Gettysburg stunted possible Confederate peace overtures.

Five days before the start of the Battle of Gettysburg, Confederate President Jefferson Davis dispatched Vice President Alexander Hamilton Stephens to negotiate a prisoner of war exchange with Lincoln under a flag of truce. Davis also gave Stephens license to proceed with broader peace negotiations.

On July 4, Stephens sat aboard a boat in Chesapeake Bay awaiting permission to sail up the Potomac. Once news of victory at Gettysburg reached Lincoln, however, he denied the Confederate vice president’s request to pass through Union lines to come to Washington, DC, for negotiations.

4. The battle bolstered badly sagging Union morale.

The spirits of a war-weary North had reached a low ebb at the beginning of the summer of 1863. The Union had endured a string of losses, and now Lee had brought the war to their territory. A loss at Gettysburg could have devastated Union morale and pressured the Lincoln administration to negotiate a peace that would have resulted in two nations. Linked with news of the victory at Vicksburg on July 4, however, Gettysburg renewed public support for the war. Davis called Gettysburg the “most eventful struggle of the war” because “by it the drooping spirit of the North was revived.”

5. Gettysburg ended Confederate enslavement of free blacks from the North.

Thousands of slaves served in support roles for the Army of Northern Virginia, and as Lee’s army marched north into Pennsylvania, they seized as many as 500 African-Americans—some former slaves, some free their entire lives—and brought them back to Virginia to be sold into slavery.

One resident of Chambersburg, Pennsylvania, reported seeing some of the town’s African Americans “driven by just like we would drive cattle,” and at least one Confederate brigade threatened to burn down any Union house that harbored a fugitive slave.

6. The battle led to the Gettysburg Address in which Lincoln redefined the Civil War as a struggle for freedom and democracy.

Land preservation efforts began immediately after the Battle of Gettysburg and resulted in a national cemetery, consecrated by Lincoln on November 19, 1863. In a mere 272 words, Lincoln’s Gettysburg Address recast the war as not merely a struggle to maintain the Union, but as a battle for larger human ideals.

Lincoln called for “a new birth of freedom” and asserted that the survival of democracy itself was at stake. He told his countrymen that the task remaining was to ensure “that government of the people, by the people, for the people, shall not perish from the earth.”

7. The battle forever transformed the town of Gettysburg.

Prior to the Civil War, Gettysburg had been a prosperous village that supported two small colleges. After the battle, however, it would forever be seared by the memories of the slaughter. In the battle’s immediate aftermath, corpses outnumbered residents of the village of just over 2,000 by four to one.

While it took years for the town to recover from the trauma, the first pilgrims arrived just days after the guns fell silent. In his book Gettysburg: The Last Invasion, Allen C. Guelzo reports that hundreds of people arrived by wagon just two days after the battle to see the carnage for themselves and that by August 1863 visitors could be found picnicking on Little Round Top amid shallow graves and rotting bodies of dead horses. Striking the balance between battlefield preservation and commercial development remains a constant debate in Gettysburg.