back then japanese cities were almost entirely made of wood with only a few main buildings being brick and mortar.  they relentlessly firebombed the japs into submission. no nukes required. its total overkill. its an old time favorite to use in war.. fire. in vietnam they had their fun with napalm. forget the nuke, its about thermobaric warheads. any city hit with enough of those will be wrecked.  and once they bust out the depleted uranium, high energy weapons and the wide array of drones. it'll be like terminator with "ufos". people are going to break and completely submit themselves to the nwo cult.
United States