Building HE is always worth it... as long as you're going to pursue a military campaign or more. You don't need to build it 30 turns before you start pumping units. It's certainly not necessary for building military police (although if you have it, might as well use it). The bottom line is: the AI doesn't care if you have 100,000 or 200,000 or 1,000,000 soldiers... to deter an attack you must have a ratio higher than a certain point. See DanF's post about DoW logic. a) if you pass the diplo test - you're safe... what's the point in having an army that costs 2000H and 40 gpt? b) if you fail the diplo test, wait until you see a WHEOOHRN activated and try to determine the target. As ~10 turns are about sufficient to prepare for an offensive war, so are 10 for a defensive war, the usual length of AI military buildup.