State one's arguments against invading land (9)
I believe the answer is:
wisconsin
'state' is the definition.
(I know that Wisconsin is a state)
'one's arguments against invading land' is the wordplay.
'one's' becomes 'i's' (Roman numeral).
'arguments against' becomes 'cons' (as in pros and cons).
'invading' means one lot of letters goes inside another.
'land' becomes 'win'.
'is'+'cons'='iscons'
'iscons' put within 'win' is 'WISCONSIN'.
(Other definitions for wisconsin that I've seen before include "Northern state" , "American state, capital Madison" , "US state, capital Madison" , "State of north central US" , "US state, capital Madision" .)