Which of these countries uses left-hand traffic?

The differentiation between U.K. LHT and France RHT goes back to The Hundred Years War. The U.K. being peaceful, knights rode on the left, so other knights approaching could see their sword hand was empty. France being in constant war, knights rode on the right with their shield between them and other knights approaching, so they could instantly defend against any attack.

When cars were invented, Henry Ford influenced the USA's driving customs because he built his first cars with the driver on the left side of the car, meaning drivers would drive on the right side of the road so their passengers could exit the car on the curb and not into oncoming traffic. Also Napoleon Bonaparte had a hand in promoting travelling on the right side of the road.

drive on left hand side or wrong side. that's your choices.

All vehicles drove on the left to begin with, as the female in the vehicle was expected to sit on the left of the male and the men would pass each other on thier right, especially in the 'wild west' where most people were armed and were right handed

I thought the advantage of LHT, historically, was that the near side of a horse is the left. The horse is always mounted left stirrup first. Which means if you mount from the pedestrian side you are heading in the right/correct direction. In US western movies, the cowboy has to turn the horse around, or go to the other side.

PresentMail7, also probably so we don't smash into each other