Final answer:
The 'high tide of the Confederacy' refers to the turning point at the Battle of Gettysburg where Confederate forces suffered a critical defeat, marking the last time Lee would attempt to invade the North and contributing to a shift in the war's momentum. The correct option is C.
Step-by-step explanation:
The term "high tide of the Confederacy" refers to the Battle of Gettysburg, which is famously known as the most pivotal battle of the American Civil War. During the battle, which occurred from July 1 to July 3, 1863, the Confederates, under the command of General Robert E. Lee, made a significant push northward into Union territory in Pennsylvania.
The battle reached a climax with Pickett's Charge, a frontal assault led by Confederate General George Pickett. Despite initial successes, the Confederate forces were ultimately repulsed, suffering heavy casualties, including over half of the men involved in the charge. Consequently, the Confederate army was forced to retreat to Virginia, making it the last time Lee attempted to invade the North.
The defeat at Gettysburg, coupled with the loss at the Battle of Vicksburg, which occurred simultaneously, marked a turning point in the war, greatly diminishing the momentum of the Confederate cause.