Not one cuisine but many: wheat and dairy in the north, rice and coconut in the south, desert thrift in the west and river fish in the east, tied together by spice sizzled in hot fat.
India's regional kitchens start with the land. The wheat plains of the north bake bread; the wet south and east grow rice; the Thar makes do with millet, lentils and what dries well; and the long coasts cook with coconut and fish. Each kitchen is also many kitchens, split by community, caste and faith as much as by map.
Faith shapes the plate. Hindu, Jain and Buddhist ideas made vegetarian cooking central across much of the country, and some communities leave out onion and garlic too; Muslim, Christian and many Hindu communities eat meat, each in their own way. Sultans and then the Mughals brought Persian and Central Asian court cooking — pilaf, kebabs, rich gravies — which settled most deeply in the north and in cities like Lucknow and Hyderabad.
Trade and empire did the rest. The spice coasts traded pepper and cardamom with Arab, Chinese and later European merchants, and chillies, tomatoes and potatoes are usually said to have arrived with the Portuguese, from the Americas, before becoming inseparable from Indian cooking. Under British rule, and after Partition, cooks moved, and restaurant food from a few regions came to stand for the whole country abroad.