Sometimes, the geographical term 'Indian subcontinent' is used interchangeably with 'South Asia', although that last term is used typically as a political term and is also used to include Afghanistan. Which countries should be included in either of these remains the subject of debate.
According to Oxford English Dictionary, the term "subcontinent" signifies a "subdivision of a continent which has a distinct geographical, political, or cultural identity" and also a "large land mass somewhat smaller than a continent". It is first attested in 1845 to refer to the North and South Americas, before they were regarded as separate continents. Its use to refer to the Indian subcontinent is seen from the early twentieth century. It was especially convenient for referring to the region comprising both British India and the princely states under British Paramountcy.
The term Indian subcontinent also has a geological significance. Similar to various continents, it was a part of the supercontinent of Gondwana. A series of tectonic splits caused formation of various basins, each drifting in various directions. The geological region called "Greater India" once included Madagascar, Seychelles, Antarctica and Austrolasia along with the Indian subcontinent basin. As a geological term, Indian subcontinent has meant that region formed from the collision of the Indian basin with Eurasia nearly 55 million years ago, towards the end of Paleocene.
The geographical region has historically simply been known as "India" (in antiquity referring to the Indus Valley region, not the entire subcontinent). Other related terms are Greater India and South Asia.
And the terms "Indian subcontinent" and "South Asia" are sometimes used interchangeably. There is no globally accepted definition on which countries are a part of South Asia or the Indian subcontinent.
The less common term "South Asian subcontinent" has seen occasional use since the 1970s.
Orthographic projection of the Indian subcontinent
Map of the Indian subcontinent
Geologically, the Indian subcontinent was first a part of so-called "Greater India", a region of Gondwana that drifted away from East Africa about 160 million years ago, around the Middle Jurassic period. The region experienced high volcanic activity and plate subdivisions, creating Madagascar, Seychelles, Antarctica, Austrolasia and the Indian subcontinent basin. The Indian subcontinent drifted northeastwards, colliding with the Eurasian plate nearly 55 million years ago, towards the end of Paleocene. This geological region largely includes Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan and Sri Lanka. The zone where the Eurasian and Indian subcontinent plates meet remains geologically active, prone to major earthquakes.
Using the more expansive definition – counting India, Pakistan, Bangladesh, Sri Lanka, Nepal, Bhutan and Maldives as the constituent countries – the Indian subcontinent covers about 4.4 million km2 (1.7 million sq mi), which is 10% of the Asian continent or 3.3% of the world's land surface area. Overall, it accounts for about 45% of Asia's population and over 25% of the world's population, and it is home to a vast array of peoples.
Historical transmission routes of Buddhism from India to Central Asia, East Asia and Southeast Asia
NASA images of the Indian subcontinent during day and night.
The Indian subcontinent is a natural physical landmass in South Asia, geologically the dry-land portion of the Indian Plate, which has been relatively isolated from the rest of Eurasia.
Given the difficulty of passage through the Himalayas, the sociocultural, religious and political interaction of the Indian subcontinent has largely been through the valleys of Afghanistan in its northwest, the valleys of Manipur in its east, and by maritime routes. More difficult but historically important interaction has also occurred through passages pioneered by the Tibetans. These routes and interactions have led to the spread of Buddhism out of the Indian subcontinent into other parts of Asia. And the Islamic expansion arrived into the Indian subcontinent in two ways, through Afghanistan on land and to Indian coast through the maritime routes on the Arabian Sea.
The Hindu Kush, centered on eastern Afghanistan, is the boundary connecting the Indian subcontinent with Central Asia to the northwest, and the Persian Plateau to the west. The socio-religious history of Afghanistan are related to the Turkish-influenced Central Asia and northwestern parts of the Indian subcontinent, now known as Pakistan. Others state Afghanistan being a part of Central Asia is not an accepted practice, and it is "clearly not part of the Indian subcontinent".
The precise definition of an "Indian subcontinent" as opposed to "South Asia" in a geopolitical context is somewhat contested.
^ abBaker, Kathleen M.; Chapman, Graham P. (11 March 2002), The Changing Geography of Asia, Routledge, pp. 10–, ISBN978-1-134-93384-6, This greater India is well defined in terms of topography; it is the Indian sub-continent, hemmed in by the Himalayas on the north, the Hindu Khush in the west and the Arakanese in the east.
^ abJohn McLeod, The history of India, page 1, Greenwood Publishing Group, 2002, ISBN0-313-31459-4; note: McLeod does not include Afghanistan in Indian subcontinent or South Asia; Jim Norwine & Alfonso González, The Third World: states of mind and being, pages 209, Taylor & Francis, 1988, ISBN0-04-910121-8 Raj S. Bhopal, Ethnicity, race, and health in multicultural societies, pages 33, Oxford University Press, 2007, ISBN0-19-856817-7; Quote: "The term South Asian refers to populations originating from the Indian subcontinent, effectively India, Pakistan, Bangladesh and Sri Lanka; Lucian W. Pye & Mary W. Pye, Asian Power and Politics, pages 133, Harvard University Press, 1985, ISBN0-674-04979-9 Mark Juergensmeyer, The Oxford handbook of global religions, pages 465, Oxford University Press US, 2006, ISBN0-19-513798-1 Sugata Bose & Ayesha Jalal, Modern South Asia, pages 3, Routledge, 2004, ISBN0-415-30787-2
^ abcdEwan W. Anderson; Liam D. Anderson (2013). An Atlas of Middle Eastern Affairs. Routledge. p. 5. ISBN978-1-136-64862-5., Quote: "To the east, Iran, as a Gulf state, offers a generally accepted limit to the Middle East. However, Afghanistan, also a Muslim state, is then left in isolation. It is not accepted as a part of Central Asia and it is clearly not part of the Indian subcontinent".
^"Asia" > Geologic history – Tectonic framework. Encyclopædia Britannica. Encyclopædia Britannica Online, 2009: "The paleotectonic evolution of Asia terminated some 50 million years ago as a result of the collision of the Indian subcontinent with Eurasia. Asia’s subsequent neotectonic development has largely disrupted the continents pre-existing fabric. The neotectonic units of Asia are Stable Asia, the Arabian and Indian cratons, the Alpide plate boundary zone (along which the Arabian and Indian platforms have collided with the Eurasian continental plate), and the island arcs and marginal basins."
^ abDesai, Praful B. 2002. Cancer control efforts in the Indian subcontinent. Japanese Journal of Clinical Oncology. 32 (Supplement 1): S13-S16. "The Indian subcontinent in South Asia occupies 2.4% of the world land mass and is home to 16.5% of the world population...."
^"Indian Subcontinent" in Encyclopedia of Modern Asia. Macmillan Reference USA (Gale Group), 2006: "The area is divided between five major nation-states, Bangladesh, India, Nepal, Pakistan and Sri Lanka, and includes as well the two small nations of Bhutan and the Maldives Republic... The total area can be estimated at 4.4 million square kilometres, or exactly 10 percent of the land surface of Asia... In 2000, the total population was about 22 percent of the world's population and 34 percent of the population of Asia."
^"Asia" > Overview. Encyclopædia Britannica. Encyclopædia Britannica Online, 2009: "The Indian subcontinent is home to a vast diversity of peoples, most of whom speak languages from the Indo-Aryan subgroup of the Indo-European family."
^"Indian Subcontinent", in Encyclopedia of Modern Asia. Macmillan Reference USA (Gale Group), 2006: "The total area can be estimated at 4.4 million square kilometres, or exactly 10 percent of the land surface of Asia... In 2000, the total population was about 22 percent of the world's population and 34 percent of the population of Asia."
^John McLeod, The history of India, page 1, Greenwood Publishing Group, 2002, ISBN0-313-31459-4 Stephen Adolphe Wurm, Peter Mühlhäusler & Darrell T. Tryon, Atlas of languages of intercultural communication in the Pacific, Asia, and the Americas, pages 787, International Council for Philosophy and Humanistic Studies, Published by Walter de Gruyter, 1996, ISBN3-11-013417-9 Haggett, Peter (2001). Encyclopedia of World Geography (Vol. 1). Marshall Cavendish. p. 2710. ISBN0-7614-7289-4.
^"the Indian Subcontinent occupies the major landmass of South Asia" John R. Lukacs, The People of South Asia: the biological anthropology of India, Pakistan, and Nepal, page 59, Plenum Press, 1984, ISBN9780306414077.
"the seven countries of South Asia constitute geographically a compact region around the Indian Subcontinent".Tatu VanhanenProspects of Democracy: A Study of 172 Countries, page 144, Routledge, 1997, ISBN9780415144063
^"Indian subcontinent" is used by Henry D. Baker, British India With Notes On Ceylon Afghanistan And Tibet (1915), p. 401.