This is a power and size comparison Xiang Ye used a 2 Kiloton or 2,000-ton nuke meaning that Kingdoms in their world are just the size of small to medium cities. Also the strongest nuke, I think their called hydrogen bombs as opposed to Xiang Ye's atom bombs, is named the Anti-Matter Bomb with 215 megatons or 215,000,000 tons of TNT.
The point is; Xiang Ye's atom bomb is the weakest nuke amongst the rest and everyone is shitting their pants or getting intimidated when he can scale it's power 8 - 25,000 times and theoretically 107,000 times more if you going by the 21st-century standard.