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; but there is a perfectly good reason. In the past, almost everybody travelled on the left side of the road because that was the most sensible option for feudal, violent societies.
In the early years of English colonisation of North America, English driving customs were followed and the colonies drove on the left. After gaining independence from England, however, they were anxious to cast off all remaining links with their British colonial past and gradually changed to right-hand driving. (Incidentally, the influence of other European countries? nationals should not be underestimated.) The first law requiring drivers to keep right was passed in Pennsylvania in 1792, and similar laws were passed in New York in 1804 and New Jersey in 1813.
Driving on the left comes from the time when people carried swords. They didn't want them to hit another person's sword when walking so they walked on the left side. Perhaps we decided on the right side just to be the opposite of the crown when we formed our nation.
The idea of driving on the left in Britain and former British colonies started because most people are right-handed. This meant that swordsmen preferred to keep to the left so as to have their right arm free and closer to an opponent and the opponent's scabbard further from him. The idea of driving on the right in the US came about as a result of using horses to haul products. Read on about this from users.telenet.be/worldstandards/driving%20on%20the%20left.htm.