Back European from part of Scandinavia Germany invaded (7)
I believe the answer is:
endorse
'back' is the definition.
(back can mean to support or endorse)
'european from part of scandinavia germany invaded' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'from part of scandinavia' becomes 'norse' (I am not sure about this - if you are sure you should believe this answer much more).
'germany' becomes 'd' (vehicle registration code for Deutschland).
'invaded' indicates putting letters inside.
'norse' enclosing 'd' is 'ndorse'.
'e'+'ndorse'='ENDORSE'
Can you help me to learn more?
(Other definitions for endorse that I've seen before include "Countersign" , "Support (with signature)" , "Add one's authority to" , "Corroborate" , "Sanction -- red nose (anag)" .)