Extreme and protracted shortage of food, resulting in widespread hunger and a substantial increase in the death rate. General famines affect all classes or groups in the region of food shortage; class famines affect some classes or groups much more severely than others; regional famines affect only a particular region of a country. Causes may be natural or human. Natural causes include drought, flooding, unfavourable weather conditions, plant disease, and insect infestation. Human causes include war, overpopulation, faulty distribution systems, and high food prices. Several severe famines occurred in the 20th century, including those in China (1928–29, at least 3 million dead; 1959–61, 15–30 million), the U.S.S.R. (1921, more than 5 million; 1932–33, 6–8 million), India (1943–44, 1.5 million), Cambodia (1975–79, 1 million), and North Korea (1995–99, 2.5 million), and continued into the 21st century, as in sub-Saharan Africa.