Sodium developed into state (6)
I believe the answer is:
nation
'state' is the definition.
(both can mean a country)
'sodium developed into' is the wordplay.
'sodium' becomes 'NA' (Na is the chemical symbol for sodium).
'developed' indicates an anagram.
'into' anagrammed gives 'tion'.
'na'+'tion'='NATION'
(Other definitions for nation that I've seen before include "The Birth of a -, D.W. Griffiths film" , "American Indian people" , "People of a country" , "A federation of tribes, as Native Americans say" , "People sharing a common culture/descent" .)