Final answer:
People gathered in Gettysburg on November 19, 1863, to attend the dedication of the Soldiers' National Cemetery and to hear President Lincoln deliver his now-famous Gettysburg Address.
Step-by-step explanation:
People gathered in Gettysburg on November 19, 1863, for the dedication of the Soldiers' National Cemetery. This event was held to honor the Union soldiers who fought and died in the Battle of Gettysburg, which was the deadliest battle of the American Civil War. The highlight of the dedication was President Lincoln's Gettysburg Address, a profound speech that redefined the American Civil War's purpose and reaffirmed the principles of freedom and equality.