The Suez Canal Opens
A hundred-mile canal cut through Egypt suddenly joined the Mediterranean to the Red Sea, halving the sea distance between Europe and Asia and making Egypt one of the most strategically vital places on Earth. Whoever controlled this thin ribbon of water controlled the shortest path between hemispheres. It was a man-made chokepoint, and it has been fought over ever since — Britain seized control of it, and Egypt's nationalization of it in 1956 triggered an international crisis.
The path or medium of exchange moves, and a place or power rises or declines because it sits on or off the new route.