The narrow, shallow channel between Sumatra and the Malay Peninsula, roughly 900 kilometers long and at its tightest only a couple of miles wide. For two thousand years it has been the dominant sea-gate between the Indian Ocean and the South China Sea, the shortest route linking the markets of India, the Middle East, and Europe to those of China and East Asia. Whoever held its key ports could tax a vast share of regional and long-distance commerce, and it remains today one of the busiest and most strategically vital waterways on earth.
Take a globe and run a finger from Europe and India toward China, and it snags on a single thin gap between Sumatra and the Malay Peninsula. Ships could go around, through the islands to the south, but that adds days and danger. So for two thousand years a large share of long-distance trade has squeezed through this channel instead. At its narrowest it is only a couple of miles wide. Through it pass roughly a quarter of the world's traded goods and much of the oil bound for China, Japan, and Korea. Whoever controlled this sliver of water grew rich on the commerce of two oceans, and a line of powers rose and fell fighting for it. The Strait of Malacca is one of the closest things the planet has to a valve on global trade.