Answer:
Because he left office peacefully and willingly.
By being the first president to leave office this way, he set a precedent and marked the first peaceful transfer of power between upcoming and current presidents. Since then, the loser of presidential elections has willingly and peacefully surrender power to the winner.
The organism "Bacillus" form spores (endospores).
Emperor Constantine made the religion, Christianity, a new, legal religion in the Roman Empire.
Lincoln would not allow slavery to the United States