Along the lines of my last statement, I recommend giving a read of
Knowing One’s Enemies – Intelligence Assessment Before the Two World Wars. The book is a collection of essays that amply illustrate the point that, even when a nation is in possession of sufficient intelligence of a quality to make effective policy decisions, it can all come to disaster due to the inherent biases, proclivities and abilities of key policy makers. The harmful effects of internal disputes within intelligence agencies, and turf battles between competing agencies, are also laid out in careful detail.
Bookmarks