About a quarter of the world drives on the left, and the countries that do are mostly old British colonies.
This strange quirk perplexes the rest of the world; however, there is a perfectly good reason.
Up to the late 1700's, everybody travelled on the left side of the road because it's the sensible option for feudal, violent societies of mostly right-handed people.
Jousting knights with their lances under their right arm naturally passed on each other's right, and if you passed a stranger on the road you walked on the left to ensure that your protective sword arm was between yourself and him.
Revolutionary France, however, overturned this practice as part of its sweeping social rethink. A change was carried out all over continental Europe by Napoleon.The reason it changed under Napoleon was because he was left handed his armies had to march on the right so he could keep his sword arm between him and any opponent.
From then on, any part of the world which was at some time part of the British Empire was thus left hand and any part colonised by the French was right hand.
In America, the French colonised the southern states (Louisiana for instance) and the Canadian east coast (Quebec). The Dutch colonised New York (or New Amsterdam). The Spanish and Portugese colonised the southern Americas. So The British were a minority in shaping the 'traffic'.
The drive-on-the-right policy was adopted by the USA, which was anxious to cast off all remaining links with its British colonial past
So there you have it!
