The Secret Service
Just hours before his death, Abraham Lincoln created the Secret Service (the men tasked with protecting the President). Perhaps with the protection afforded to future Presidents by the Secret Service, Lincoln would have lived that fateful night in Ford Theater.
The Motives of the Assassin
John Wilkes Booth killed Abraham Lincoln to liberate the South from what he saw as harsh Union rule. However, the death of Lincoln caused a tremendous amount of strife -- and likely resulted in harsher Union rule -- in the South.
Lincoln: A John Wilkes Booth Fan?
Lincoln used to be a fan of John Wilkes Booth, the actor, before Booth killed him.
Lincoln and Andrew Johnson's Bodyguard
Abraham Lincoln, one of the most important and powerful men in the world, went unprotected because his single bodyguard was drinking. Andrew Johnson, his successor, was saved from assassination because his would-be assassin was drinking.
Dr. Samuel Mudd
Dr. Samuel Mudd, who took the Hippocratic Oath and vowed to only help people, aided John Wilkes Booth in the death of Abraham Lincoln.