Final answer:
The Battle of Gettysburg was a significant turning point in the Union's favor (c), marking the end of Confederate invasions to the North and leading to a shift in the war's momentum.
Step-by-step explanation:
The Battle of Gettysburg was significant because it was a turning point in the Union's favor (c). This pivotal battle, which lasted from July 1 to July 3, 1863, marked the end of Confederate General Robert E. Lee's second and most ambitious invasion of the North. Notably known for its high casualty rates and brutal confrontations, such as Pickett's Charge, the Union victory at Gettysburg halted Confederate momentum and made a profound impact on the course of the American Civil War.
After the first day of fighting at Gettysburg, the Union forces took a defensive position along the crest of hills below the town, which gave them a valuable advantage. Over the next two days, Confederate forces -- under General Lee's command -- launched fierce attacks against both flanks and the center of the Union lines. Despite determined efforts, these assaults were repelled, culminating in the disastrous Pickett's Charge against the Union center on Cemetery Ridge, resulting in massive Confederate casualties and a forced retreat of Lee's army back to Virginia. These events marked the "High Watermark of the Confederacy" -- essentially the closest the Confederate forces came to achieving a potentially war-changing victory.
Specifically, the Union success at Gettysburg, along with the capture of Vicksburg, Mississippi on the same day, fundamentally shifted the momentum of the war. It discouraged foreign intervention on the side of the Confederacy and boosted Union morale. President Abraham Lincoln further cemented the significance of the battle with his renowned Gettysburg Address, which paid tribute to the Union soldiers who had given their lives and reiterated the purpose of the Civil War.