Right hand Drive vehicles at USA Airports

A little of topic, but does anyone know why some countries drive on the left side of the road. I was once given a reason by a bunch of British guys when we were working together in Germany. It made perfect sense to me.

Most countries that drive on the left have been linked to Britain/UK in one way or another.

Provided that I don’t scolded for going off topic, I will give the reason in a few days.