Difficulties include the existence of intercontinental missiles, cruise missiles and drones. All not yet existing at the start of WW2. Also the unknown probability that any incoming are suspected of being nuclear weaponised. Invaders and occupiers depend on lots of refined oil products for transport logistics. It follows that defence strategy will attack major sites of oil refining and supply of their enemies by any or all remote means. Another major war will cripple the global black gold world exploitonomy, and all its networked dependencies. The super rich want to hold that power over everyone, but don’t want to light the fuse.