This particular strain of military insanity had as its Patient Zero one Giulio Douhet, an Italian aviation pioneer whose career strongly resembled that of his American counterpart Billy Mitchell. Basing his theories on his experiences in the Italo-Libyan War and the First World War, Douhet predicted that future wars would be wars of mutual annihilation in which bombers would ravage the centers of production until war could not be continued. (This would be called Mutual Assured Destruction once people got around to theorizing about strategic nuclear warfare.) Douhet's theories were seized on by military aviators in many nations, most notably England and the United States, to justify separate military forces for air warfare. As noted elsewhere, though, military technology didn't stand still. Anti-aircraft artillery and interceptor fighters were developed to attack and kill the heavy bombers, many of which had not been designed with defensive guns in accordance with the theory that the bombers would simply fly too fast and too high for guns or enemy fighters to reach them.
This theory failed horribly in practice during the Second World War, forcing the RAF to resort to hideously inaccurate night bombing and the U.S. Air Force to hurriedly redesign the B-17 to carry a plethora of defensive machine guns. Both services also developed long-range fighters to serve as escorts for the heavy bombers.
Having learned nothing from the loss of hundreds of B-17 bombers during the Second World War, the U.S. Air Force proceeded to develop more strategic bombers in accordance with Douhet's theories: the XB-70A Valkyrie was the ultimate expression of this line of development, and was scrapped only when it was realized that the Soviets had surface-to-air missiles which could easily reach the Valkyrie at its operational altitude. The disease persists nonetheless since political considerations prevent the deployment of antiballistic missile defenses, thus transferring the psychosis to ballistic missiles instead of bombers.