Question

why we had caste in india

Answer 1

Because Indians have the abilities and authority to know the capacity of a person. Like census.

Answer 2

In India the works were divided among people. For example-Some people used to teach children, some had a task to provide security while some had a work of cleaning roads,toilets etc. Later their next generation also continued the same job. And due to this these people got divided into different division.After this some of them dominated the others and hence castes formed.
I hope it would help.