Okay, let’s get the obvious one out of the way - because everyone else is doing it . I did some searching on this, but haven’t come up with anything.
I know (or think I know) why we drive on the left. The majority of people passing will have their sword hands on the side of the stranger. Antiquated (if true), but at least it’s a reason that explains why the convention started.
So what’s the US’s (and pretty much the rest of the world’s) excuse?
I’m sorry to say this, but reading Cecil’s answer made me realise that even the sun has its spots and the master isn’t infallible.
For some reason Swedish, pre-switch-to-right cars, had their steering wheels on the left side (wich made the change very smooth). The only Swedish made cars with the steering wheel on the right side were made for export to other leftside driving countries.