Final answer:
John Wilkes Booth was a Confederate sympathizer who assassinated President Abraham Lincoln, leading to national mourning and impacting the course of Reconstruction.
Step-by-step explanation:
The historical significance of actor John Wilkes Booth is that he assassinated President Abraham Lincoln. On April 14, 1865, Booth, a Confederate sympathizer, shot Lincoln during a play at Ford's Theater in Washington. The act of assassination was a part of a larger conspiracy aiming to disrupt the Union government and continue the Confederate cause, with Booth and his associates also targeting other key figures like Secretary of State William Seward. Lincoln's assassination had profound effects on the nation, causing widespread mourning and serving as a catalyst for heightened tensions during the Reconstruction era.