What was the single most important factor that forced the Indian government to introduce a new set of policy measures in 1991?

External debt crisis

In 1991, India met with an economic crisis relating to its external debt — the government was not able to make repayments on its borrowings from abroad; foreign exchange reserves , which we generally maintain to import petroleum and other important items, dropped to levels that were not sufficient for even a fortnight. The crisis was further compounded by rising prices of essential goods. All these led the government to introduce a new set of policy measures which changed the direction of our developmental strategies.