The first cure involved a ceasefire (5)
I believe the answer is:
truce
'a ceasefire' is the definition.
(I know that truce is a type of ceasefire)
'the first cure involved' is the wordplay.
'the first' becomes 't' (1st letter of 'the').
'involved' is an anagram indicator (involved can mean confusing or complex).
'cure' with letters rearranged gives 'ruce'.
't'+'ruce'='TRUCE'
(Other definitions for truce that I've seen before include "move towards permanent peace" , "Agreement to suspend fighting" , "peace initiative" , "Peace agreement" , "halt in fighting" .)