system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do some countries drive on the left and some on the right

Why isn't there a universal driving  system?
gpt
35% of the worlds's population drives on the left, mainly the UK and her more recent former colonies.  
The reason was so that a person could either show their right hand was empty or draw a weapon with their right hand and prepare to defend themselves.

65% of the world's population drives on the right.
The stated reason was teamsters who hauled freight by horse in France and America. They didn't have seats to save on weight, they would sit on the left rear horse, so they could whip any horse with their right hand. So they preferred people pass them on the left so they could make sure their wheels were clear.