Roughly a third of the world's population drives on the left side of the road. The reason traces back centuries before cars existed, to a time when which side of the road you used could genuinely protect your life.
Most people throughout history have been right-handed. Swordsmen kept to the left side of the road specifically so their right arm, and their weapon, stayed closer to any oncoming stranger, while their scabbard stayed safely out of reach on the far side.
Mounting a horse reinforced the same habit. A right-handed rider finds it far easier to mount a horse from its left side, which meant horses were naturally led and ridden along the left edge of the road as well.
Right-side driving has a very different, much more political origin. Some historians trace the switch to pre-revolutionary France, where aristocrats traveled on the left, forcing peasants to the right side of the road.
During the French Revolution, that dynamic flipped entirely. The aristocracy began moving to the right side of the road to avoid standing out, and right-side travel became official policy in Paris by 1794.
A separate shift happened across the ocean around the same era. American freight wagons pulled by multiple horses had no driver's seat, so drivers rode the rear-left horse to control the team with their right arm, which naturally pushed traffic toward the right side of the road.
One car changed everything for the rest of the world. Henry Ford's mass-produced Model T placed the steering wheel on the left side of the car, making right-side driving far more practical and helping cement it as the global standard for most of the automotive era.
