AFAIK everyone used to drive on the correct left hand side of the road <img src="/images/graemlins/wink.gif" alt="" />. This was based on the fact that people walked past each other on that side to keep it easy to draw a sword. It was easy just to continue the habit on to horses, carriages then cars.

Napoleon was left handed. He therefore wanted his soldiers to pass him on the other side <img src="/images/graemlins/crazy.gif" alt="" /> <img src="/images/graemlins/grin.gif" alt="" />(egomaniac - surely not). Therefore he changed the etiquette to suit himself. Logically this then continued to the present day for the same reasons and the French drive on the right.

Everywhere the Brits went people drive on the left and everywhere the French went people drive on the right. The significant exceptions (no Brits or French colonisation or trade) such as Switzerland and Japan also drive (quite sensibly IMHO <img src="/images/graemlins/tongue.gif" alt="" />) drive on the left since again most people would be right handed and therefore want to freely draw swords unemcumbered when meeting people.

OK, now we get to the USA. When we Brits were in charge you rode and drove carriages on the left. After some squabbling over taxation you changed. Just so that you could be different. When Mr. Ford invented the motor car he of course made it to drive on the right. When other countries imported cars who were not previously committed to left or right handed roads (or didnt have roads!) they also imported driving on the right.

Seems reasonable. I am going to be so dissapointed though if that bit about Napoleon is an urban myth though!