Some 76 countries and territories use left-hand traffic, and the practice is believed to have originated in ancient Rome to help defend against enemy attacks.

Following is a transcript of the video.

Why do some countries drive on the left side of the road? Most of the world drives on the right side of the road. But around 76 countries and territories use left-hand traffic.

The practice is believed to date back to ancient Rome. Romans steered their carts and chariots with the left hand, to free up the right so they could use weapons to defend against enemy attacks.

This carried over into medieval Europe and in 1773, the British government passed measures to make left-hand traffic the law. But postrevolution France favored the right.

Napoleon was left-handed, and riding on the right proved to be an intimidating military tactic. Britain and France brought their driving styles to their respective colonies. That's why many former British territories are among the few modern left-hand-traffic countries.

In the US, right-hand traffic goes back to the 18th century. Freight wagons were pulled by teams of horses. and the drivers rode on the left rear horse, using their right hand to more easily control the team. Traffic shifted to the right so drivers could easily avoid collisions.

Eventually, with the rise of the automobile and increase in global traffic, many countries switched to the right to fit in with neighbors — including Samoa, which just switched from the left in 2009.

This video was originally published on December 2016.