As the historian Peter Kincaid describes it, the reason why you drive on the right or left today has to do with two things. The first is that most people are right-handed. The second is that different countries were using different forms of transportation at the time that formalized rules the road began to emerge.
The way in which the first consideration intersected with the second consideration explains how we drive today.
Thus a Samurai in Japan, who kept his scabbard on his left side and would draw with his right arm, wanted to be on the left as he passed potential enemies on the road. So Japan today drives on the left.
In England, horse-drawn carts were generally piloted by drivers mounted in the seat. The mostly right-handed drivers would “naturally” sit to the right, holding the reins in the left hand and the whip in the right. The driver could better judge oncoming traffic by traveling on the left. So England drives on the left.
But in many other countries, including the United States, a driver often walked along the left side of his horse team or rode the left horse in a team (the left-rear horse if there were more than two), so that he could use his right arm for better control. This meant it was better to stay to the right, so he could judge oncoming traffic and talk to other drivers. The result is that many countries today drive on the right.