Threatening fury in party over United States (9)
I believe the answer is:
dangerous
'threatening' is the definition.
(thesaurus)
'fury in party over united states' is the wordplay.
'fury' becomes 'anger' (fury is intense anger).
'in' indicates putting letters inside.
'party' becomes 'do' (do is a kind of party).
'over' means one lot of letters go next to another.
'united states' becomes 'US' (abbreviation for the United States).
'anger' going inside 'do' is 'dangero'.
'dangero'+'us'='DANGEROUS'
(Other definitions for dangerous that I've seen before include "menacing" , "Not safe" , "Hazardous" , "posing a threat" , "Harmful, injurious" .)