It depends on what kind of castle you mean.
If you mean a castle from a fantasy story, dragons and/or enemy knights could threaten a castle.
If you mean a toy block/LEGO castle, then just stepping on it or dropping it threatens it.
If you mean a real-life castle, then a bomb or something like a bomb could threaten it.
you should leave him if your boyfriend threatens you in anyway your to good for him so ditch him NOW
people
tadpoles
I did
people
tadpoles
Human
this! :-D
When War Threatens - 1914 was released on: USA: 4 August 1914
drylands
People
Habitat destruction