United is related to Organization. Unit is a type of Organization. Unit is related to Empire. Empire is related to King. 
you are likely to find Explosion in/at/on Universe. Universe is related to Evolution. 
United <--RelatedTo--> Organization <--IsA-- Unit <--RelatedTo--> Empire <--RelatedTo--> King 
Explosion --AtLocation--> Universe <--RelatedTo--> Evolution 