The famines were a product both of uneven rainfall and British economic and administrative policies. Colonial policies implicated include rack-renting, levies for war, free trade policies, the expansion of export agriculture, and neglect of agricultural investment. Indian exports of opium, rice, wheat, indigo, jute, and cotton were a key component of the economy of the British empire, generating vital foreign currency, primarily from China, and stabilising low prices in the British grain market. According to Mike Davis, export crops displaced millions of acres that could have been used for domestic subsistence and increased the vulnerability of Indians to food crises. Others dispute that exports were a major cause of the famine, pointing out that trade did have a stabilizing influence on India's food consumption, albeit a small one