Information about own forces, allied forces and opposing forces has always been a key feature of military operations, discussed in Sun Tzu's The Art of War:
If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.
Nations, corporations, and individuals each seek to increase, protect and exploit their own information while trying to limit and penetrate the adversary's. Methods to collect, store, analyse and exploit information cover the whole range of both military and commercial activities and whilst this discussion is related to the military application of the discipline these methods legitimately apply in the commercial environment.
Since the 1960s, there have been extraordinary improvements in the technical means of transmission, protection, collection, storage and analysis which have allowed significant improvements in the exploitation of the information domain.