Germany collapse after victory -- that's a bonus (8)
I believe the answer is:
windfall
'a bonus' is the definition.
(windfall is a kind of bonus)
'germany collapse after victory' is the wordplay.
'germany' becomes 'd' (international vehicle registration code).
'collapse' becomes 'fall' (I've seen this before).
'after' is a charade indicator (letters next to each other).
'victory' becomes 'win' (I've seen this before).
'd'+'fall'='dfall'
'dfall' put after 'win' is 'WINDFALL'.
'that's' is the link.
(Other definitions for windfall that I've seen before include "Bonus not expected" , "Piece of luck (but it might be bruised)" , "bonanza" , "Lucky acquisition" , "An unexpected piece of luck - maybe an apple" .)