The first rhinos lived about 50 million years ago. During the Miocene, around 20 million years ago, there were maybe 30 different species of rhinos. In the period before, Oligocene, several predecessors died out. At the time, rhinoceros animals were much more common than today. Today, the hunt for their horns are the biggest problem and to read about the hunt for Rhinos for horns sake is a depressing story. Around the year 1900 there were only about 20 individuals left of the so-called white rhino in South Africa. They were protected in a national park in South Africa. The southern white rhino was considered for a while extinct until a number was found in 1895, Thanks to 100 years of efforts to preserve them, there are now over 20 000 in South Africa, a success story. http://www.savingrhinos.org/White-Rhino.htm
These white rhinos have been reintrodused in Botswana, Namibia, Swaziland, Zimbabwe, Kenya, Zambia and Cote d'Ivoire. Recently a calf was born even in Uganda but the hunt for horns is problematic. The coveted horns are used in Chinese and Vietnamese medicine and to handle daggers in Oman and Yemen. The use of daggers has been reduced but the use in Chinese medicine seem to increase.
Below is a diagram of rhinos killed in South Africa. South Africa has about 95% of all African rhinos. Lately they have started introducing them in the Okavango Delta which have very good control over some areas. At one time, these rhinos were prevalent in the area.