Because of desertification
what do you mean by marginal lands?
Nearly half of it.
Yes, in the antebellum South, many regions were divided into large farm lands called plantations that primarily cultivated cash crops such as cotton, tobacco, rice, and sugar cane. These plantations were worked by enslaved African Americans and were owned by wealthy landowners who controlled the production and labor on the estates.
To provide much needed labor to farm the lands for cotton and tobacco - to supply the British Empire.
The Kalahari Desert covers much of Botswana and the Namib Desert is on the west coast of Namibia.
It may make life warmer for some living in very cold climates, and some areas will be able to grow more crops. But many of the present farm lands may become unusable. Droughts as well as floods may make people's lives much more difficult.
there is one lake in the savanna grass lands
It is a huge continent, with a wide variety of countries and geographic conditions. Some parts are difficult to live in. A lot of the northern part of Africa is the Sahara Desert, the world's largest desert. So there is little there to survive on. It is the same in some of the other deserts in Africa. A lot of Africa is jungle, which can be difficult to live in too. There are a lot of open plains in Africa, where not a lot can grow. It is important to mention that a lot of Africa is not difficult to live in. Many parts are well developed, with large cities and good living conditions or good ground to grow crops in and with weather that is not difficult to live in. There is poverty in some of those parts, much as there is in any part of the world, but there are a lot of people living very good lives.
How much it rains on a farm depends entirely on where the farm is. If the farm is in Pennsylvania, for example, or Florida, it will get a lot more rain than a farm in the Central Valley of California.
Greece was mountainous so it was difficult to farm though i know they were able to plant grapes. They were able to farm on very little land. If you want a more specific answer you should search it on google, you'll probably find a page about greece there. Hope this helped :)
Farm products in Riverside County are quite diverse. So much so that a primary crop or product might be a bit difficult to isolate. See the related link below.