Wagon centre in history (3)
I believe the answer is:
'in history' is the definition.
(I've seen this in another clue)
'wagon centre' is the wordplay.
'centre' means to look at the middle letters.
The middle of 'wagon' is 'AGO'.
(Other definitions for ago that I've seen before include "(Years) before the present time" , "Previously" , "Back (in time)" , "Earlier, gone by" , "Gone, past, since" .)