A monarch is deposed in Zimbabwe (8,5)
I believe the answer is:
victoria falls
'in zimbabwe' is the definition.
('Victoria Falls' is part of 'zimbabwe')
'a monarch is deposed' is the wordplay.
'a monarch' becomes 'Victoria' (Queen Victoria).
'is deposed' becomes 'falls' (I can't justify this - if you can you should give a lot more credence to this answer).
'victoria'+'falls'='VICTORIA FALLS'
Can you help me to learn more?
(Other definitions for victoria falls that I've seen before include "Tourist attraction of the Zambezi" , "drop of water" , "Current attraction" , "Italian sports-car company" , "Zambezi River spectacle" .)