I've been listening to an audio lecture on Global Geopolitics and the professor mentions how the Strait of Malacca was and is one of the most important points in international trade. The country that controlled the strait could control a large part of global trade flows. Looking at the area on Google Maps, I can see why it's so important. At the same time, due to the archipelagic nature of the region, I can think of a number of possible alternatives that could have broken Malacca's monopoly on passage. For instance, why couldn't ships pass through the strait between Indonesia's Jakarta and Badar Lampung? It's a bit longer in distance, but I can't imagine the cost of the detour to be prohibitive. Similarly, there a number of potential passage points between the big Indonesian islands. Why didn't these options really take off compared to the Strait of Malacca? Surely, as a big trader nation, the Dutch would have loved having a big trading hub in their colony?
Another alternative I considered is Thailand: I have read about recent plans for a canal through Thailand's peninsula, but why was this never realized in the past? Surely Thailand and countries that didn't control the Strait of Malacca would have had quite a bit to gain if such a canal would have come to fruition?
There have been plans to cut a canal through southern Thailand, dating back as far as the 1670s. Several routes have been proposed for it. (It's often called the Kra Canal project, as the isthmus is called the Kra Isthmus.)
During the period I'm most familiar with, the British East India company had investigated several routes. After Burma became a British colony, Britain and Thailand agreed to drop any canal plans to protect the harbor of Singapore. That agreement has stood, uneasily, until the present day. (There have also been more recent activities in the peninsula relating to building a canal in the area, but it would violate the 20-year-rule to talk about them.)