Why does India drive on the left?

About a third of the world drives on the left, including India, the UK, Japan and Australia. The rest drive on the right. Why the split?

In the days of horses and swords, most people were right-handed. Riding on the left kept your sword arm towards anyone coming the other way, and you mounted a horse from the left. So keeping left was the natural old rule across Europe.

Then France changed sides after its revolution, and Napoleon spread right-hand driving across the countries he conquered. Britain, which he never conquered, kept left — and passed the habit to its colonies, including India.

India kept the rule after Independence. Switching sides is expensive and dangerous; Sweden did it in 1967 and needed years of planning for a single day.