Which is not a possible reason for the decline of great zimbabwe?

a) shifting trade routes
b) overgrazing
c) disease
d) the end of the slave trade

the end of the slave trade

Explanation: i say this cause this zimbabwe is a ruined city

D. The end of slave trade.

Explanation:

Great Zimbabwe was the capital of Kingdom of Zimbabwe and the people of Great Zimbabwe controlled the trade between inland Africa and the coast. Historians claim that they were Karanga people which were branch of Shona-speaking people. Cattle production and gold were the source of wealth for rulers of Great Zimbabwe.  

There are various theories about the decline of Great Zimbabwe, Environmental change and Migration are believed to be the cause for their decline.  According to the environmental theory drought and overgrazing exhausted the soil of Zimbabwe plateau and it would have led to the famine.  

The other explanation is that the the people migrated to maximise the exploitation of golds trade network and abandoned the site of Great Zimbabwe around 1500 AD, the people moved towards the north and south.