Throughout the 1920's and early 1930's there were serious and not so serious political or diplomatic efforts to eliminate aerial bombing (and in some cases military aviation altogether). These ranged from proposals to replace all national air forces with an international air force maintained by the League of Nations, a Hague treaty setting firm limitations on the scope of aerial bombing, and as late as 1932 the Geneva Disarmament Conference considered a variety of proposals ban or significantly reduce air forces. Some of these proposals actually had solid support within the military establishments of a number of major powers - usually centered around conservative army and navy leadership.
Beginning no earlier than 1923 create a timeline leading in 1939 to a WW2 including a Germany under the Nazis in which none of the major powers have air forces capable of offensive bombing, either against civilians or military targets. You may allow naval aviation, presuming that by treaty, carrier-based planes can only participate in naval actions and scouting. For an added bonus, imagine how the war would play out - including the possibility that, starting essentially from scratch, some or all combatant powers might, after 1940, begin developing airforces, lacking any training in the doctrines of air power and probably with militarily less capable aircraft.
Beginning no earlier than 1923 create a timeline leading in 1939 to a WW2 including a Germany under the Nazis in which none of the major powers have air forces capable of offensive bombing, either against civilians or military targets. You may allow naval aviation, presuming that by treaty, carrier-based planes can only participate in naval actions and scouting. For an added bonus, imagine how the war would play out - including the possibility that, starting essentially from scratch, some or all combatant powers might, after 1940, begin developing airforces, lacking any training in the doctrines of air power and probably with militarily less capable aircraft.