Abraham Lincoln (1865)

John Wilkes Booth's assassination of Abraham Lincoln on 14 April 1865—just five days after Lee's surrender—removed the one leader capable of implementing a moderate Reconstruction, producing consequences that lasted a century. Lincoln's successor, Andrew Johnson, blocked civil rights legislation, enabling the Jim Crow system of legal segregation that endured until the 1960s. This assassination's impact on American race relations far outweighs that of #4 John F. Kennedy's in terms of structural, long-term damage: Jim Crow laws disenfranchised millions and shaped inequality for generations. The 13th Amendment had already passed, but without Lincoln, its promise of freedom went largely unfulfilled for African Americans in the South.