Kept from being unhappy about a historic day (5)
I believe the answer is:
saved
'kept from' is the definition.
(saving is a kind of keeping from)
'unhappy about a historic day' is the wordplay.
'unhappy' becomes 'sad' (similar in meaning).
'about' is an insertion indicator.
'a historic day' becomes 've' (I can't justify this - if you can you should give a lot more credence to this answer).
'sad' enclosing 've' is 'SAVED'.
'being' acts as a link.
Can you help me to learn more?
(Other definitions for saved that I've seen before include "Rescued; put by" , "Kept for later" , "what Jesus did" , "Stored for future use" , "Redeemed or stored" .)