700 years ago everybody used the English system, and if distressing numbers of us have proven fickle in the centuries since, that’s no reason to dump on the Brits.
In the Middle Ages you kept to the left for the simple reason that you never knew who you’d meet on the road in those days. You wanted to make sure that a stranger passed on the right so you could go for your sword in case he proved unfriendly.
This custom was given official sanction in 1300 AD, when Pope Boniface VIII invented the modern science of traffic control by declaring that pilgrims headed to Rome should keep left.
The papal system prevailed until the late 1700s, when teamsters in the United States and France began hauling farm products in big wagons pulled by several pairs of horses. These wagons had no driver’s seat. Instead the driver sat on the left rear horse, so he could keep his right arm free to lash the team. Since you were sitting on the left, naturally you wanted everybody to pass on the left so you could look down and make sure you kept clear of the other guy’s wheels. Ergo, you kept to the right side of the road. The first known keep-right law in the U.S. was enacted in Pennsylvania in 1792, and in the ensuing years many states and Canadian provinces followed suit.
In France the keep-right custom was established in much the same way. An added impetus was that, this being the era of the French Revolution and all, people figured, hey, no pope gonna tell ME what to do. Later Napoleon enforced the keep-right rule in all countries occupied by his armies. The custom endured even after the empire was destroyed.
The trend among nations over the years has been toward driving on the right, but Britain has done its best to stave off global homogenization. Its former colony India remains a hotbed of leftist sentiment, as does Indonesia, which was occupied by the British in the early 19th century. The English minister to Japan achieved the coup of his career in 1859 when he persuaded his hosts to make keep-left the law in the future home of Toyota and Mitsubishi.
Nonetheless, the power of the right has been growing steadily. When Germany annexed Austria in 1938, it brutally suppressed the latter’s keep-left rights, and much the same happened in Czechoslovakia in 1939. The last holdouts in mainland Europe, the Swedes, finally switched to the right in 1967 because most of the countries they sold Saabs and Volvos to were righties and they got tired of having to make different versions for domestic use and export.
The current battleground is the island of Timor. The Indonesians, who own west Timor, have been whiling away the hours exterminating the native culture of the east Timorese. The issue? Some say it’s religion, some say it’s language, but I know the truth: in east Timor they drive on the right, in west Timor they drive on the left.