It all comes down to history, horses, and Napoleon.
For centuries, most travelers rode or drove on the left. Long before automobiles, people traveled on horseback or in horse-drawn carriages. A warrior riding on the left kept the right hand free to draw a sword if an enemy approached, making left-side travel the safer instinct for the largely right-handed population. Britain formalized this in the 1773 Highways Act (often called the Keep Left law), and its empire spread the habit to India, Australia, New Zealand and beyond—making left-hand traffic prevalent across much of the Commonwealth.
The shift right traces to Napoleon, who standardized right-side travel across conquered Europe for logistical uniformity and to reject British norms as a political statement amid intense rivalry and near-constant war with Britain. The United States followed right-side driving, influenced by French wagon design and manufacturing scale.
Today, one-third of the countries drive on the left and rest on the right—a divide still shaped by colonial legacy and revolutionary politics.
