The struggle to the first on Earth, possibly? (6)
I believe the answer is:
strife
'the struggle' is the definition.
(strife is a kind of struggle)
'the first on earth possibly?' is the wordplay.
'on' is a charade indicator (letters next to each other).
'earth' becomes 'e'.
'possibly?' is an anagram indicator (I've seen 'possibly' mean this).
'first' after 'e' is 'efirst'.
'efirst' is an anagram of 'STRIFE'.
'to' is the link.
(Other definitions for strife that I've seen before include "'Discord, conflict (6)'" , "Trouble and discord" , "Lack of harmony" , "Heated discord" , "Discord and friction" .)