They need water supplies and some food and they can make do
The Northern Kalahari was 'settled' by the apartheid government to form a buffer against any potential invasion from the north (Russian/Cuban etc plus the ANC and its friends) in the 60s and 70s. The primary input needed was access to water, so the government ran water pipelines into the region, some measuring over 300km, and gave farmers a water allocation per livestock unit per day. That scheme persists to this day, although the current government and its allergy to maintenance is resulting in water supply getting more erratic amd the Kalahari is slowly 'de-populating'.
Farmers were given large tracts of land with the expectation that they would farm it on a use it or lose it basis. Farmers that were seen to be making adequate developments and acceptable usage of the land were offered additional tracts - hence the formation of some very extensive farms.
Anyway the upshot of all this was the creation of a water distribution network to water small livestock and the game in the area benefitted enormously. Animals not endemic to the region like warthog have migrated there - their ability to burrow under fences and also unearth and bite open plastic water pipes helped. Much to the farmers' aggravation. So now warthogs are present and a scourge to farmers.
Similar story with kudu migrating into arid areas of the Karoo, where they were previously unknown/uncommon. Irrigation schemes have facilitated both water and food for species that are able to either go over or under fences.
Most of the game redistribution into semi-arid and arid areas was the result of human introduction but in some cases it happened by itself.
