The indigo plant grows primarily in the tropics and this was the primary reason for the British to turn to India for the growth of the indigo plant.
By the thirteenth century Indian indigo was being used by cloth manufacturers in Italy, France and Britain to dye cloth.
The demand for Indian indigo grew, as European cloth manufacturers wanted only Indian Indigo as it produced a rich blue colour. Due to this demand the price of Indian indigo rose in the European market and mediated the British to grow more indigo in the Indian soil.
Another reason was the industrialisation of Britain as this resulted in the expansion of cotton production creating an enormous new demand for cloth dyes.
Indigo production in other countries began to decline and the demand for Indian Indigo increased in European countries. This demand made the East India Company to expand the area under indigo cultivation.