Historically, people have always preferred to travel on the left side of the road. In medieval times, swordsmen would prefer to ride/walk on the left side, so their right arm was closer to a possible enemy, if they encountered one.
On the continent it was Napoleon who introduced right side driving and subsequently spread the practice to all conquered areas.
The British obviously stuck with left side driving, while also exporting the practice to their colonies.
Source: https://www.worldstandards.eu/cars/driving-on-the-left/