Why do cars drive on the left in Japan, the UK and her former colonies, and on the right everywhere else?

Question

I'm NOT saying one is better than the other, just curious.
This convention must have started early, because railway trains observe the same rule. London must have been crowded enough for some basic traffic rules before American cities like New York were settled by English people, but New York drives on the right! So do other large, old cities like Rome. Did people drive their buggies wherever they liked until automobiles appeared? What chaos that must have been!

Answer 1

http://users.pandora.be/worldstandards/driving%20on%20the%20left.htm