It was Napoleon who has handed down the right hand lane driving, all of europe (and the US) adopted it as it would be difficult to change lanes passing across borders. Always thought that with manual cars the british system was better as the usually stronger right hand was always on the wheel. Sweden changed to the Continental system many years ago after an extensive public awareness programme and a lot of new traffic control measures such as relaying junctions, new signage etc. They changed at midnight and the first person caught driving on the wrong side was a lorry driver, 6 minutes after the change. When question by police he said he had nothing about it.

Actually Qatar did drive on the other side until the arrival of the American Oil companies who presented the important people with a fleet of Buicks. The Emir changed the system overnight to the US model. Dont know what happened at the changeover