Why did the French call Napoleon "Napo?"

Okay, listen up, buttercup. The joke is a play on words. "Napo" is short for Napoleon, and the punchline is "Because it is Napo[leon]" implying that "Napo" is part of the full name Napoleon. You probably didn't know that Napoleon was a famous French military leader and emperor in the 19th century. Bet you feel dumb now, huh?