Cut down trees + monsoon = no soil
This happened in Ethiopia, from around ~600 AD to 800 AD. Ethiopia is a giant volcanic plug sticking up two kilometers from the African Savanna. Because of its height and position right at the edge of the tropics, it had an excellent combination of stable year round temperatures, cold enough nights to prevent tropical diseases from spreading (malaria was minimal and tsetse flies non-existant), and stong, albeit seasonal, rainfall.
This meant two things: not only did Ethiopia have its own set of native crops, it was also to import and grow a wide variety of crops from other places. Ethiopia initially thrived. The hills were covered in forests, so there was plentiful wood, rich volcanic soil, and lots of lakes and rivers from rainfall. This is one of the few patches of Harenna forest remaining in Ethiopia.
The Axumite empire flourished in the 4th to 6th centuries. In the time before Islam, it was considered one of the great powers of the near East, rivaling Persia. Axumite armies expelled the Persians from modern day Yemen in 525 AD.
But things went wrong (and this is covered in Jared Diamond's Collapse). They cleared their mountainous home of trees to expand farmland and population. Ethiopia has a monsoon-like climate. Addis Abebe recieves about 1200 mm of rain each year, roughly the same as New York City, but 50% of the rain falls in just 2 months. Addis Abeba sees more rain in July and August than London, San Francisco, or Beijing see all year. in other words, a monsoon climate.
Denuded of tree cover, the heavy summer rains washed the available topsoil away. The rich volcanic soil that had built up over 30 million years was eroded away, leaving scrubby brush and barren ground. The change happened relatively quickly. Trees along riverbanks were the last to be cut, since riverbanks aren't great places to farm. But once you decide to cut those trees to fire your forge or cooking fire, erosion proceeds rapidly. From the apex of power in the late 6th century, the Axumites had fallen so far that their capital was practically abandoned less than 50 years later.
Ethiopian civilization did not die, of course. It continues to the present day, with almost 100 million people still living on the plateau. But the fertile ground that had propelled the Ethiopians to imperial ambitions was relegated to the dustbin of history.