Unhappy season in America leading to collapse (8)
I believe the answer is:
downfall
'collapse' is the definition.
(thesaurus)
'unhappy season in america leading' is the wordplay.
'unhappy' becomes 'down' (I've seen this before).
'season in america' becomes 'fall' (US name for autumn).
'leading' says to put letters next to each other.
'down'+'fall'='DOWNFALL'
'to' acts as a link.
(Other definitions for downfall that I've seen before include "(Cause of) ruin" , "Ruin, humiliation" , "Ruin; heavy shower" , "burst of rain" , "state of ruin" .)