I've heard a lot about how brutal cave fighting was on islands like Iwo Jima and Okinawa during WW2. What was it about those battles that made it important to clear out so many caves by hand? Why was it not possible to simply seal off any caves they found?
The Japanese had months of preparation and plenty of soldiers, machine guns, mortars, and artillery. In both cases, the areas involved were simply too small to just seal off and ignore - the range of the guns in such a small area precluded it.
For example, on Iwo Jima, they needed the airfields to launch fighters to protect bombers from Saipan (and prevent the Japanese from basing fighters there) - meaning they couldn't leave enemy artillery on the island.