Maps the introduction of totalitarianism, finally (2,4)
I believe the answer is:
at last
'finally' is the definition.
(synonyms)
'maps the introduction of totalitarianism' is the wordplay.
'maps' becomes 'atlas' (printed collection of maps).
'the introduction of' suggests taking the first letters.
The initial letter of 'totalitarianism' is 't'.
'atlas'+'t'='AT LAST'
(Other definitions for at last that I've seen before include "In the end, after much delay" , "Where a snob worked" , "Finally, after much delay" , "'In the end (2,4)'" , "None too soon" .)