A mess with car crashing and carnage! (8)
I believe the answer is:
massacre
'carnage' is the definition.
(thesaurus)
'a mess with car crashing' is the wordplay.
'with' says to put letters next to each other.
'crashing' indicates anagramming the letters.
'a'+'mess'='amess'
'amess' put after 'car' is 'caramess'.
'caramess' is an anagram of 'MASSACRE'.
'and' is the link.
(Other definitions for massacre that I've seen before include "Complete defeat" , "Large-scale indiscriminate killing" , "Destroy" , "Slaughter, holocaust" , "Brutal slaughter" .)