Back in the apartheid days, Cuban troops were massing in Angola and the implication was that they would push through Namibia and "liberate" South Africa. A test site was set up in the desert for an atomic bomb. This site was clearly visible to spy satellites and implied to those watching that an invasion would be met with a nuclear response. As the invasion didn't proceed, it appears to have been decided at higher levels that it wouldn't be a good idea. An Israeli style ultimate deterrent.