Declaration in the year peacekeepers unite (12)
I believe the answer is:
announcement
'declaration' is the definition.
(announcement is a kind of declaration)
'in the year peacekeepers unite' is the wordplay.
'in the year' becomes 'anno' (I've seen this before).
'peacekeepers' becomes 'UN' (United Nations, peacekeeping organisation).
'unite' becomes 'cement' (I've seen this in another clue).
'anno'+'un'+'cement'='ANNOUNCEMENT'
(Other definitions for announcement that I've seen before include "report" , "Public notice" , "Statement, declaration" , "Public declaration" , "Proclamation" .)