Question

what is the reason for subsidiary alliance by wellesly

Answer 1

by creating enimiest among indian rulers by the british

Answer 2

this alliance was made after winning the battle of palsy so that the rulers of these independent states could do no harm to the east India company.

According to this alliance, all the rulers will be working independently under the British rule, they cannot form any treaty or alliance with any other ruler nor  form their own Army the eat India company will protect them and they have to pay for its security.