And now I know! Thanks for the info! I had no idea.Have you ever noticed in cop shows and movies when there is a car chase the pursuing car driver blasts away with a handgun but never hits anything? That's because he's sitting on the WRONG side of the car (the left) for a usually right handed person to aim properly. In fact that's why we do it the other way round this side of the pond. In the days of stage coaches travelling between towns and cities (pre industrial revolution, well let's face it pre America!), the custom was to pass a carriage or rider coming the other way to their and your right, so that if they had hostile intent you could draw your sword or flintlock with your right hand to defend yourself.
Americans drive on the right because of the Teamsters, back in the day, they drove a cart and horses by riding one of the team of horses on the left, as the cart usually had no seat (Hollywood make believe again). You'd sit on the left to hold the reins in your right hand predominantly and so the custom to pass others to your left became established. Now you know!
My earlier comment was my go-to joke when I meet a British. I apologize if I've offended you in any way.