Almost everywhere around the globe, people drive on the right-hand side of the road. Except for Great Britain, some of its former colonies and Japan, who drive on the left. How did that come about? It turns out, there’s a perfectly sensible explanation.
During the middle ages the roads weren’t always very safe for travelers; meeting people coming the other way on the road was something best done defensively. Historians then believe the keep-left rule was adopted because, on a horse, if you were right handed and you met some unsavory company on the road, you could draw your weapon, typically attached to your left side, with your right hand and bring it to bear quickly against the person who is going the opposite way of you on your right; all the while, controlling the reigns with your left hand. Then of course, if you happened to meet a friend on the road, you could more easily offer your right hand in greeting without needing to reach across your body when on horseback. People on horseback then also typically ruled the road, so everybody else followed suit.
This keep-left rule was so common that, in 1300 AD, Pope Boniface VIII decreed that all pilgrims headed to Rome from wherever they were coming from should abide by the keep-left rule of the road along their journey. This then held across most of the Western World until the late 1700s.
What ended up happening to force the switch in the 18th century were teamsters in the United States, who would drive large wagons with a team of horses, as the name implies. These wagons tended to dominate the road and force everybody else to abide by the rule of the road they were using. Very importantly, in many of those old, large American wagons, they did not include a seat on the wagon for the driver. Rather, the driver would typically sit on the rear left most horse, when the driver was right handed. This allowed them to easily drive a whole team of horses with a lash in their right hand.
So feudal societies got in the habit of being on the left, so they hand their right hand free for Road Rash style beatings if necessary and to keep their scabbard away from others and it was because of the Teamsters that everyone else drives on the right.
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