Office of Strategic Services,look it up if you want a RL example to see how and why an extremely effective organization, that was vital to a war effort, can be decimated, torn down and reorganized into a shadow of it's former self.
Extremely bad and inappropriate example. First of all OSS was formed during the wartime for a sole purpose to support the war and had a very short life. It did not have any real infrastructure. A lot of intelligence came from other organizations and various resistance movements. In many cases all it did was steal the credit for the information. And most importantly OSS did not have any role in internal security. Its dissolution had no affect because after the war it became redundant. As I stated before, a proper example for Imperial Intelligence would be NKVD or SS. While a modern example would be CIA and FBI in one.