Dagen H
It’s a country’s prerogative to change its mind. "Dagen H" (3 September 1967) was the day that Sweden switched from driving on the left hand side to the right.
The reason why cars (and indeed people) in most countries keep to the right, but in some countries keep to the left, relates to the passage of horses and horse-drawn carriages, and a general desire to have a rider’s greeting/sword-carrying hand (right for a horse rider, but left for a carriage d…