The British used to collect rent from Indian farmers. They used to collect other taxes also. They fixed the year as of April to March for all these tax collections. That is how this financial year has come in to force.
There are about 156 countries in the world that are following their financial year from January 1 to December 31. About 33 countries, including India, have their financial year from April 1 to March 31. There are 20 countries following their accounting year from July 1 to June 30.