Cheetahs face a number of threats, mostly from human interaction. As humans expand, with new cities, roads, and other developments, the cheetah's habitat shrinks. This is extremely challenging when populations are separated from each other, since they have far more trouble finding others to breed with, leading to further population reductions. Farmers and poachers are also a threat, as they will often kill a cheetah to protect their farm animals, or to sell the fur on the black market.
Life is difficult for a predator that isn't designed to be at the top of the food chain, either. Cheetahs face dangers from other predators, such as lions, hyenas, and other creatures that are larger and stronger, and who often like to steal their prey.
Another challenge is that cheetahs have very little genetic diversity. Scientists speculate that the population suffered a huge setback during the last ice age, reducing their numbers significantly, as well as their gene pool. Since the cheetah is also a highly specialized animal, built for speed in an open environment, it has trouble adapting to new environments.
The good news is that there are over 12,000 cheetahs estimated to be living in the wild, which makes it safer than other big cats such as the tiger, and conservation efforts such as the Cheetah Conservation Fund and the Cheetah Conservation Foundation, as well as other multinational groups, have been working to save the species. Since cheetahs are extremely popular with safari groups, they are also quite useful to the ecotourism industry, so countries have lots of reasons to try to save the cheetah.